America's dire prediction: "Putin will not stop the war, unless..."

On that occasion, he also expressed doubts about Putin's willingness to negotiate in good faith.

"There's not much that would lead us to believe in that at this point," Petraeus said when asked if such a meeting would take place.

"In fact, in the last two weeks ... I think it should be clear to everyone, and I think it's clear even to President Trump, that despite all his efforts ... to end the war, to stop the killing, Vladimir Putin clearly has no intention of doing it except in one case, and that is to gain additional territory, which Russian forces would have to fight for years at this rate."

He added that Putin's fundamental demands - including a pro-Russian government in Ukraine and its demilitarization - have not changed. "The obstacle to peace at the moment is President Putin," he said.

Petraeus argued that the US and its allies must change the balance of power by increasing military and other support for Ukraine.

"What we have to do is change that dynamic by helping Ukraine much more than we have done so far," he said.

"Remove restrictions, take away 300 billion dollars of frozen Russian cash reserves in European countries, give the same amount of money to Ukraine. More sanctions on Russia, including even Gazprom Bank, to further restrict oil exports than we have already done."

Petraeus' comments followed two weeks of intense diplomatic activity. Trump and Putin met face-to-face in Anchorage, Alaska on August 15.

With Ukraine excluded from the Alaska summit, Zelensky, accompanied by a delegation of European leaders, traveled to Washington on August 18 to meet with Trump and insist on concrete security guarantees in the event of a future peace agreement with Moscow. After the meetings, Trump said that a bilateral summit between Zelensky and Putin could take place within two weeks.

However, recent statements by Russian officials indicate that such a meeting remains unlikely.