Retired general David Petraeus predicts the US would destroy Russia's military in Ukraine and sink its naval fleet if it used nuclear weapons

If Putin used nuclear weapons, the US and its allies would destroy Russia's military forces in Ukraine and sink its Black Sea fleet.

In an interview with ABC News on Sunday, Petraeus, who served as CIA director and commander of coalition forces in Iraq, said that the US would respond to a nuclear attack by Russia.

"Just to give you a hypothetical, we would respond by leading a NATO, a collective effort that would take out every Russian conventional force that we can see and identify on the battlefield in Ukranian and in the Black Sea," said Petraeus.

When asked if the use of nuclear weapons by Russia would bring the US and its allies into the war, Petraeus was cagey about whether nuclear radiation from an attack on NATO states could be considered an attack on them.

He suggested that you could make that case. There has to be a response because this is so horrible.

You don't want to escalate the situation here. You have to prove that this can't be accepted.

The annexation of several regions in east Ukraine by Russia was announced by Putin last week and he threatened the use of nuclear weapons. After Ukraine regained control of large tracts of territory from Russia, the Kremlin called for a mass deployment of military and civilian personnel.

The moves were described as desperation.

He said that the battlefield reality he is facing is irreversible. No amount of shambolic mobilization, no amount of annexation, and no amount of veiled nuclear threats can get him out of this situation.

At some point, there will have to be recognition of that. President Zelenskyy has said that at some point there will need to be a beginning of negotiations.