The US evaluates scenarios in the face of Putin's nuclear threat 1:01
(CNN) --
US President Joe Biden issued a stern warning Thursday about the dangers behind Russian President Vladimir Putin's nuclear threats as Moscow continues to face military setbacks in Ukraine.
“For the first time since the Cuban missile crisis, we have a direct threat of the use of a nuclear weapon if, in fact, things continue the way they are,” Biden warned during remarks at a Democratic fundraiser in New York, where he was introduced by James Murdoch, the youngest son of media mogul Rupert Murdoch, according to the group's report.
What are tactical nukes and what would happen if Russia deployed one?
He added: "I don't think there is such a thing as being able to easily use a tactical nuclear weapon and not end up in Armageddon."
Should we be worried about Putin's threats to use nuclear weapons?
1:50
It is striking that the President speaks so bluntly and invokes Armageddon, particularly at a fundraiser, while his aides, from the National Security Council to the State Department to the Pentagon, have spoken in much more measured terms, saying that they take the threats seriously, but do not see in them a move by the Kremlin.
“I'm trying to figure out what Putin's off-ramp is,” Biden said during the event: “Where will he find an exit?
Where will he find himself in a position where he not only loses face but he loses significant power within Russia?
His comments come as the US assesses how to respond to a variety of potential scenarios, including fears that the Russians could use tactical nuclear weapons, according to three sources briefed on the latest intelligence and previously reported by CNN.
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Officials warned Thursday that the United States has detected no preparations for a nuclear attack.
Yet experts see them as potential options the US must prepare for as Russia's invasion falters and Moscow annexes more Ukrainian territory.
"This rattling of nuclear sabers is reckless and irresponsible," Pentagon spokesman Gen. Pat Ryder said early Thursday.
"As I mentioned before, at this stage, we do not have any information that would cause us to change our strategic deterrent posture, and we do not assess that President Putin has made the decision to use nuclear weapons at this time."
Would Russia use nuclear weapons to defeat Ukraine?
2:52
Following Biden's comments, officials reiterated to CNN Thursday night that they had seen no change in Russia's nuclear posture.
A US official said that despite Biden's warning that the world is the closest it has come to a nuclear crisis since the 1960s, they have so far not seen a change in Russia's nuclear posture.
Tuesday's statement by White House Press Secretary Karine Jean-Pierre that there has been no indication of a change in Russia's position, and therefore no change in the US position, is yet to be holds, the official said.
A senior US government official expressed surprise at the president's comments, saying there were no obvious signs of a growing threat from Russia.
While there is no doubt that Russia's nuclear posture is being taken seriously, this official said the president's language at a fundraiser tonight caught other government officials off guard.
"Nothing was detected today that would reflect an escalation," said the official, who went on to defend Biden's comments due to the current seriousness of the matter.
At the fundraiser, Biden was clearly speaking out about the threat officials believe Russia poses, a person familiar with his thinking told CNN.
Still, US officials have taken note of the Russian president's repeated public threats to use nuclear weapons.
In a televised speech late last month, Putin said: “If the territorial integrity of our country is threatened, we will certainly use all available means to protect Russia and our people.
I'm not bragging."
Last Friday, at a ceremony announcing the illegal annexation of four Ukrainian regions, Putin said Russia would use "all available means" to defend the areas, adding that the United States had "created a precedent" for nuclear strikes. in the bombings of Hiroshima and Nagasaki in World War II.
“We have a guy that I know pretty well,” Biden said of Putin on Thursday.
"He's not kidding when he talks about the potential use of tactical nuclear weapons or biological or chemical weapons because his military, you could say, is significantly underperforming."
CNN's Jim Sciutto and Jeff Zeleny contributed to this report.
Nuclear weapons
