Former CIA director and retired four-star army general David Petraeus warned on Sunday that if Russian President Vladimir Putin uses nuclear weapons in Ukraine, US and its allies would destroy Russia’s troops and equipment as well as sink its Black Sea fleet.

Petreaus said that he had not discussed the anticipated US response to a nuclear escalation from Russia with national security adviser Jake Sullivan, even though administration officials claim that this response has been frequently expressed to Moscow, The Guardian reports.

“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 Ukraine and also in Crimea and every ship in the Black Sea,” Petreaus told ABC News.

Read: Ukraine says Russia smuggling its grain; Moscow says allegation “baseless”

The development comes days after Putin made comments that many regarded as a threat to escalate tensions between Russia and the west into a full-scale war.

When asked if the use of nuclear weapons by Russia in the Ukraine would include the United States and NATO in the conflict, Petreaus responded that such an event would not fall under the provisions of Article 5 of the alliance, which calls for a collective defence. Despite the fact that Ukraine is not a member of NATO, Petreaus claimed that a “US and NATO response” would be appropriate, the Guardian report says.

Petreaus claimed that Putin was “desperate” as a result of rising pressure after Ukrainian successes in the country’s east under the annexation declaration issued last week and mounting internal opposition to mobilisation efforts.

Read: Impact of Russia-Ukraine War on Asia’s climate goals

The ex-CIA director emphasised that things might still grow worse for Putin and Russia. And nothing will alter this, not even the tactical use of nuclear bombs in Ukraine, he said. “You have to take the threat seriously,” he, however, noted.