Alexei Navalny, the Russian opposition leader believed to have been poisoned, said in an interview Sunday that he was on a flight from to Moscow from Siberia in August when he realized what had occurred.

"I said to the flight attendant, and I kind of shocked him with my statement, 'Well, I was poisoned and I'm going to die,'" he told CBS' "60 Minutes" correspondent, Lesley Stahl.

The plane made an emergency landing in Siberia, where he was hospitalized for two days until the Russian government let him travel to a Berlin hospital. He spent 32 days in the hospital – 24 of them in intensive care – before doctors OK'd his release.

BEING NAVALNY: RUSSIAN ACTIVIST, WIFE EXPLAIN HIS BRUSH WITH DEATH AFTER POISONING, ESCAPING FOR TREATMENT

This handout photo published by Russian opposition leader Alexei Navalny on his Instagram account shows himself, center, and his wife Yulia, right, daughter Daria, and son Zakhar, top left, posing for a photo in a hospital in Berlin, Germany. (Navalny Instagram via AP)

Navalny said his team in Siberia searched his hotel room, where they found the nerve agent, said to be Novichok, on a bottle from the hotel.

Toxicology reports from labs in France and Sweden confirmed a German Military lab's findings that he was poisoned by military-grade Novichok, believed to be ten times more potent than sarin gas.

Navalny, one of Putin's fiercest critics, accused Russian intelligence services, and the president himself, of poisoning him with the nerve agent, which has been linked to other attacks that Western officials suspect were carried out by agents in the country.

"[There is a] huge cover-up operation," Navalny told Stahl. "There is no criminal investigation so far. If Putin is not responsible, why there is no investigation?"

KREMLIN CRITIC ALEXEI NAVALNY SAYS PUTIN RESPONSIBLE FOR POISONING IN NEW VIDEO INTERVIEW

"I don't think, I'm sure that he's responsible," he continued.

Putin spokesman Dmitry Peskov said the charge was "completely baseless and unacceptable."

Navalny, however, said the Russians "deny everything" because it means they still have the nerve gas. 

On Monday, the European Union agreed to impose sanctions against Russian officials over the incident, according to the New York Post.

"Well, all these leaders have signed on, except Donald Trump," Stahl said.

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"Yes, I-- I have noticed it," Navalny responded. "I think it's extremely important that everyone, of course, including and maybe in the first of all, president of United States, to be very against using chemical weapons in the 21st Century."

Fox News' Barnini Chakraborty contributed to this report