U.S. President Donald Trump said he was "not done" with Russian President Vladimir Putin, according to a BBC interview published on Tuesday, hours after he said he was disappointed in Putin and threatened Moscow with sanctions.

Trump told the BBC he thought a Ukraine deal was on the cards with Russia four different times.

Asked then by the BBC was he done with Putin, Trump said: "I'm disappointed in him , but I'm not done with him. But I'm disappointed in him".

Pressed on how Trump would get Putin to "stop the bloodshed" the U.S. president said: "We're working it".

"We'll have a great conversation. I'll say: 'That's good, I'll think we're close to getting it done,' and then he'll knock down a building in Kyiv," Trump told the BBC.

Trump announced new weapons for Ukraine on Monday and threatened sanctions on buyers of Russian exports, with a 50-day grace period, unless Russia agreed to a peace deal, a major policy shift brought on by frustration with Moscow's ongoing attacks on its neighbor.

He told reporters on Monday that billions of dollars of U.S. weapons, including the Patriot air defence missiles, will be sent to Ukraine via NATO and that NATO would pay for them.

Since returning to the White House promising a quick end to the war, Trump has sought rapprochement with Moscow, speaking several times with Putin. His administration has pulled back from pro-Ukrainian policies such as backing Kyiv's membership in NATO and demanding Russia withdraw from all Ukrainian territory.

But Putin has yet to accept a proposal from Trump for an unconditional ceasefire, which was quickly endorsed by Kyiv. Recent days have seen Russia use hundreds of drones to attack Ukrainian cities.

In the BBC interview, Trump expressed renewed support for the NATO alliance.

"I think NATO is now becoming the opposite of that (obsolete) because the alliance was "paying their own bills", he told the BBC.