Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

President Joe Biden made some of his most clear and striking assessments on Russian President Vladimir Putin’s threats of using a nuclear weapon.

For the "first time since the Cuban missile crisis, we have the direct threat of the use of a nuclear weapon if in fact things continue down the path that they are going. That’s a different deal," he said at a fundraiser in New York City on Thursday.

"We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis," he said. "I don't think there's any such thing as the ability to easily [use] a tactical nuclear weapon and not end up with Armageddon."

Biden said Putin's military is "underperforming" in Ukraine and he may feel threatened.

Biden said he knows Putin "fairly well" and has spent "a fair amount of time with him" and warned that Putin is serious.

"He is not joking when he talks about potential use of tactical nuclear weapons, or biological, or chemical weapons because his military is, you might say, significantly underperforming," Biden said.

"There’s a lot at stake," Biden said. "We are trying to figure out what is Putin’s off ramp? Where does he get off? Where does he find a way out? Where does he find himself in a position that he does not - not only lose face but lose significant power within Russia?"

-ABC News' Justin Gomez

There are mines along the perimeter of Zaporizhzhia, Europe's largest nuclear power plant, the head of the International Atomic Energy Agency, Rafael Grossi, said at a press conference in Kyiv Thursday after holding talks with Ukrainian President Volodymyr Zelenskyy. The facility is currently under the control of Russian forces.

"There have been indications that in the perimeter of the plant there are some mines, yes," Grossi said, before denying that there are any mines inside the plant itself.

Grossi is headed to Russia next to push for a security zone to be set up around the Zaporizhzhia plant.

Grossi told reporters that the IAEA considers Zaporizhzhia a Ukrainian facility.

"I think the IAEA, as an international organization, has a mission, has a legal parameter to do it. And what I will be is very consistent as I have been from the very beginning. We are not changing our line. We are continuing saying what needs to be done, which is basically avoid a nuclear accident. At the plant, which is still a very, very clear possibility. Yes," Grossi said.

-ABC News' Brittyn Clennett

The village of Hrekivka in Ukraine's Luhansk region has been liberated, its governor, Serhiy Haidai, said Friday, adding that fierce fighting continues for other settlements.

"I’ve seen some soldiers already posted a photo of them standing on the background of the sign 'Hrekivka,' so its not a secret anymore — it is already liberated. And we keep moving in that direction," Haidai said.

"After liberating Lyman [in Donetsk at the end of last month], as expected, the main battles are on the direction of Kreminna. The occupiers are pulling their main forces there. This is where the beginning of de-occupation of Luhansk oblast lies," Haidai said.

He added, "Luhansk region liberation will be tougher than Kharkiv region. All those Russian military who ran from Kharkiv region and Lyman ran to our direction, so the occupation forces increased in number."

-ABC News' Will Gretsky

Russian forces struck a residential neighborhood in the southeastern city of Zaporizhzhia early on Thursday, officials said.