Five European allies on Saturday (February 14) blamed Russia of killing late Kremlin critic Alexei Navalny using a toxin from poison dart frogs - an accusation rejected by Moscow - but how does the toxin work?

WHAT HAVE EUROPEAN ALLIES SAID

In a joint statement, Britain, France, Germany, Sweden and the Netherlands said analysis of samples from Navalny's body "conclusively" confirmed the presence of epibatidine, a toxin found in poison dart frogs in South America and not found naturally in Russia.

Britain said the poisoning demonstrated "an alarming pattern of behavior." The country held a public inquiry into the poisoning in Britain of Russian double agent Sergei Skripal in 2018. It concluded last year Russian President Vladimir Putin must have ordered the Novichok nerve agent attack.

HOW HAS RUSSIA REACTED

The Kremlin on Monday rejected accusations from five European countries that the Russian state had killed late Kremlin critic Alexei Navalny two years ago using toxin from poison dart frogs, saying the claims were "not based on anything."

Kremlin spokesman Dmitry Peskov told reporters on Monday (February 16) that Moscow took a very negative view of the European allegations, which he said were false.

Russian authorities, who have outlawed Navalny's movement as extremist, have previously rejected accusations from his widow, Yulia Navalnaya, that the state had killed him, saying he died of natural causes.

HOW STRONG IS THE TOXIN

Dr. Eric Franssen, a clinical pharmacologist and toxicologist, told Reuters that the toxin is very potent, adding that less than half a milligram of the compound can be deadly for a human being of 70 kilograms.

The poison can be extracted from the skin of dart frogs, Franssen said, but in principle it can also be synthesized in a lab from raw materials. However Franssen said that it's a complex process to create the toxin from the raw materials.

HOW IS THE TOXIN DETECTED POST-MORTEM

Franssen said that toxins can normally be detected through comprehensive toxicology screenings of blood and urine samples, as well as analysis of organ tissues - for example, the lungs, heart or live - after autopsy. It is also possible to calculate the concentration of the toxin through organ analysis, and ascertain if a lethal amount was ingested.

HOW IS THE TOXIN ADMINISTERED

Franssen told Reuters that the most straightforward away to administer the toxin is a direct injection into the bloodstream, as it will act immediately. However it can be ingested via the stomach, but more is needed to make the toxin effective, Franssen said.

DESCRIPCIÓN DE IMÁGENES

VIDEO SHOWS: INTERVIEW WITH CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN / FILE OF RUSSIAN OPPOSITION POLITICIAN ALEXEI NAVALNY / FILE OF RUSSIAN POLITICIAN AND NAVALNY'S WIFE, YULIA NAVALNAYA / FILE OF POISON DART FROGS

SHOWS: ST. PETERSBURG, RUSSIA (FILE - FEBRUARY 16, 2024) (REUTERS - Access all)

1. VARIOUS OF FLOWERS AND PORTRAITS OF OF RUSSIAN OPPOSITION POLITICIAN ALEXEI NAVALNY AFTER ANNOUNCEMENT OF HIS DEATH

2. PEOPLE LAYING FLOWERS

GRAPHIC (FILE) (NATIONAL INSTITUTES OF HEALTH/PUBCHEM - Must on screen courtesy 'National Institutes of Health/PubChem)

3. 3D IMAGE OF EPIBATIDINE COMPOUND

KHARP, YAMAL-NENETS REGION, RUSSIA (FILE - DECEMBER 28, 2023) (REUTERS - Access all)

4. ENTRANCE OF IK-3 PENAL COLONY, WHERE NAVALNY WAS HELD

5. HOUSES NEAR IK-3 PENAL COLONY

KHARP, YAMAL-NENETS REGION, RUSSIA (FILE - DECEMBER 29, 2023) (REUTERS - Access all)

6. IK-3 PENAL COLONY BUILDING

MUNICH, GERMANY (FEBRUARY 14, 2026) (TV4 SWEDEN /JONA KÄLLGREN - No use Sweden)

7. NAVALNY’S WIFE, YULIA NAVALNAYA, AND EUROPEAN MINISTERS SITTING ON CHAIRS IN FRONT OF REPORTERS

8. (SOUNDBITE) (English) SWEDISH FOREIGN MINISTER, MARIA MALMER STENERGARD, SAYING:

“Experts from our countries have been able to find out how Alexei Navalny was poisoned."

9. MEDIA FILMING

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

10. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

“The toxin interacts with the central and peripheral nervous system in the body. So this means that the respiratory muscles become paralyzed and you become cardiac. Also, the heart is affected. So ultimately, you do not have enough oxygen, and this is for the brain, not very good. So you will have coma and death as a result of the paralysis of the respiratory muscles in combination with heart failure.”

MUNICH, GERMANY (FEBRUARY 14, 2026) (TV4 SWEDEN /JONA KÄLLGREN - No use Sweden)

11. NAVALNAYA DURING NEWS CONFERENCE

12. (SOUNDBITE) (English) WIFE OF ALEXEI NAVALNY, YULIA NAVALNAYA, SAYING:

"Now it's not just words, it's scientific proof that my husband, Alexei Navalny, was poisoned and killed by Russian government and by Vladimir Putin in Russian prison."

OMSK, RUSSIA (FILE - AUGUST 22, 2020) (REUTERS - Access all) (ORIGINALLY 4:3) (MUTE)

13. VARIOUS STILL PHOTOGRAPHS OF NAVALNY BEING CARRIED INTO AMBULANCE

BERLIN, GERMANY (FILE - JANUARY 17, 2021) (REUTERS - Access all)

14. KREMLIN CRITIC, ALEXEI NAVALNY, ENTERING PLANE AHEAD OF RETURNING TO RUSSIA

MOSCOW, RUSSIA (FILE - JANUARY 17, 2021) (VIDEO OBTAINED BY REUTERS - Access all)

15. NAVALNY TALKING TO POLICE AT BORDER CONTROL / NAVALNY KISSING HIS WIFE YULIA, WALKING AWAY WITH POLICE

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

16. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

“The drug has also analgesic compounds, so they try to make a real drug of it for therapeutic purposes. And above five micrograms per kilogram, it is too toxic for animals and humans. So it's a very potent toxin, which can be deadly for a human being of seventy kilograms, for instance, within less than half a milligram of the compound.”

UNKNOWN LOCATION (FILE - RELEASED SEPTEMBER 17, 2025) (ORIGINALLY SHOT IN PORTRAIT) (YULIA NAVALNAYA - No Resale/ No Archive/ Mandatory Onscreen Credit Yulia Navalnaya)

17. (SOUNDBITE) (English) ALEXEI NAVALNY'S WIDOW, YULIA NAVALNAYA, SAYING (SOUNDBITE CONTINUES OVER STOCK FOOTAGE OF LABORATORIES):

“In February 2024, we were able to obtain samples of Alexei's biological material and securely smuggle them abroad. Labs in at least two countries examined these samples independently of each other, and these labs, in two different countries, reached the same conclusion. Alexei was killed. More specifically, he was poisoned.”

MOSCOW, RUSSIA (RECENT - FEBRUARY 9, 2026) (REUTERS - Access all)

18. VARIOUS OF KREMLIN

MOSCOW, RUSSIA (FILE) (REUTERS - Access all)

19. STILL PHOTOGRAPH OF KREMLIN SPOKESMAN DMITRY PESKOV

AUDIO ONLY: UNIDENTIFIED LOCATION (FEBRUARY 16, 2026) (REUTERS - Access all)

20. (SOUNDBITE) (Russian) KREMLIN SPOKESMAN, DMITRY PESKOV, SAYING (PLEASE NOTE SOUNDBITE OVERLAYS SHOT XX) (ASKED ABOUT KREMLIN'S REACTION TO ACCUSATIONS OF POISONING ALEXEI NAVALNY):

"(We react) very negatively. Naturally, we do not accept such accusations. We disagree with them. We consider them biased and unfounded. And, in fact, we strongly reject them."

MOSCOW, RUSSIA (RECENT - FEBRUARY 9, 2026) (REUTERS - Access all)

21. KREMLIN WALL AND TOWERS

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

22. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

"You can isolate it from the skins of these frogs. That's one possibility. And the other possibility is that you synthesize it in a chemical lab from all kinds of raw materials. It's a very complex chemical synthesis. In the lab, it takes multiple steps to go from the raw material to the ultimate toxin. But in principle, it can be synthesized."

UNKNOWN LOCATION (FILE) (TROPICAL TUTORIALS VIA YOUTUBE - Must on-screen courtesy Tropical Tutorials via YouTube)

23. VARIOUS OF EPIPEDOBATES ANTHONYI, A SPECIES OF POISON DART FROG, IN TANK

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

24. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

"With regard to the detection in post-mortem material, normally we collect blood and urine from deceased people, and then you can do comprehensive toxicology screenings or targeted screenings for compounds in toxicology labs, for instance. You can also collect tissues after autopsy, for instance, the lungs, the heart, or the liver. And then you can identify toxins in these organs as a first step. You may also quantitate the amount. So you can measure concentrations and when these concentrations are high, then it's very likely that you ingested much toxins and that it can be lethal."

UNKNOWN LOCATION (FILE) (TROPICAL TUTORIALS VIA YOUTUBE - Must on-screen courtesy Tropical Tutorials via YouTube) (MUTE)

25. VARIOUS OF FROGS IN TANK

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

26. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

"The measurements are normally done in blood, urine, and tissues. However, when you only focus on this toxin, you may not know if it has been synthesized in a lab or if it's isolated from animals or, like skins in the case of the dart frog. So you cannot distinguish. What you could do is that you can also look for other toxins that are present in the frog. Then you have more clues that it may come from isolation instead of chemical synthesis."

UNKNOWN LOCATION (FILE) (TROPICAL TUTORIALS VIA YOUTUBE - Must on-screen courtesy Tropical Tutorials via YouTube) (MUTE)

27. FROGS IN TANK

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

28. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

"You die because you have less oxygen, but you are completely conscious. So that is not very pleasant. And there have been reports from animal studies that you can die within ten to twenty minutes. When you have less oxygen, your brain and you are in a coma, and then you can die. So the cause of death may be correlated with the amount of oxygen in the brain."

SYDNEY, AUSTRALIA (FILE - FEBRUARY 12, 2001) (REUTERS - ACCESS ALL) (MUTE)

29. STILL PHOTO OF A SOUTH AMERICAN POISON DART FROG,AT SYDNEY'S TARONGA ZOO

AMSTERDAM, THE NETHERLANDS (FEBRUARY 15, 2026) (REUTERS - Access All)

30. (SOUNDBITE) CLINICAL PHARMACOLOGIST AND TOXICOLOGIST, DR. ERIC FRANSSEN, SAYING:

"We do not know very much about the potentials to administer it, but the most ideal way of getting high exposure is by direct injection into the bloodstream, because then it can act immediately. However, it can also be ingested, but when it is ingested, it needs to pass the stomach and the toxin may be inactivated then. So you need more of the toxin to be effective. And it may also have some skin penetration, but there are very few scientific reports to support this."

UNKNOWN LOCATION (FILE) (TROPICAL TUTORIALS VIA YOUTUBE - Must on-screen courtesy Tropical Tutorials via YouTube)

31. FROGS IN TANK