"I don't think much about Vladimir Putin," Biden told reporters at the White House when asked about the Russian president's warning that giving Kyiv the green light would mean that NATO was "at war" with Moscow.

Starmer was set to press Biden during the meeting to back his plan to send British Storm Shadow missiles to Ukraine to hit deeper inside Russia as allies become increasingly concerned about the battlefield situation.

"I think the next few weeks and months could be crucial, very, very important, that we support Ukraine in this vital war of freedom," Starmer said as the talks began.

But while Biden said it was "clear that Putin will not prevail in this war," he is expected to reject Ukraine's demand to be able to use long-range US-made ATACMS missiles against Russian territory.

US officials believe the missiles would make a limited difference to Ukraine's campaign and also want to ensure that Washington's own stocks of the munitions are not depleted.

- 'Afraid' -

The White House played down the chances of any immediate decision coming from Friday's visit by Starmer, the Labour leader's second to the White House since he took office in July.

"I wouldn't expect any major announcement in that regard coming out of the discussions, certainly not from our side," National Security Council spokesman John Kirby told reporters.

Ukrainian President Volodymyr Zelensky however pushed Kyiv's Western allies to do more.

Speaking in Kyiv, Zelensky accusing the West of being "afraid" to even help Ukraine shoot down incoming missiles as it has done with Israel.

Zelensky added that he will meet Biden "this month" to present his "victory plan" on how to end two and a half years of war with Russia.

He also said Kyiv's recent offensive into Russia's border region of Kursk had "slowed" Moscow's advance in eastern Ukraine.

Russia has reacted angrily to the prospect of the West supplying long-range weapons to the country it invaded in 2022.

In another sign of increasing tensions, Russia revoked the credentials of six British diplomats whom it accused of spying in what London termed "baseless" allegations.

Kremlin spokesman Dmitry Peskov said Putin's war warning on Thursday was unambiguous: "We have no doubt that this statement has reached its recipients," he said on Friday.

Russia's UN ambassador Vassily Nebenzia warned separately that letting Ukraine use long-range weapons would plunge NATO into "direct war with... a nuclear power."

- Trump fears -

Ukraine and the United States's allies are all meanwhile anxiously waiting for the result of a tense US presidential election in November that could upend Washington's Ukraine policy.

Biden is on his way out of office while the election is a toss-up between his Democratic political heir Kamala Harris and Republican former president Donald Trump.

Trump has repeatedly praised Putin, and refused to take sides on the war during a debate with Harris on Tuesday, saying only: "I want the war to stop."

Trump has also repeatedly pledged to push through a quick deal to end the war if elected -- a deal many Ukrainians fear would force them to accept Russia's territorial gains.

Biden has strongly supported Ukraine since Russia's invasion, but has been risk averse about stepping up to new kinds of weapons deliveries, fearful of stoking nuclear tensions with Putin.

His reticence about allowing Ukraine to use longer-range US missiles follows similar delays on HIMARS rockets, tanks and F-16 jets -- all of which he eventually approved.

Harris has pledged to continue steadfast support for Ukraine if elected.

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