The US says it is preparing "robust responses" over fears of a Russian invasion of Ukraine, after President Biden's rare talks with Vladimir Putin.

In a video link, Mr Biden voiced deep concerns over Russian troop build-ups and threatened "strong economic and other measures", Washington said.

Russia says it will not attack Ukraine.

Mr Putin accused Kyiv of provocation, and sought guarantees against eastward Nato expansion and deployment of offensive weapons close to Russia.

The talks began at 10:07 US Eastern time (15:07 GMT; 18:07 Moscow time), the White House said.

They were held on a secure video link set up under previous administrations but never used before, Russian news agency Tass said.

Video footage of the opening moments showed friendly greetings between the US and Russian leaders. The talks then continued behind closed doors, lasting about two hours.

Mr Putin held the talks from his residence in the southern resort of Sochi, according to Tass.

After Tuesday's video call, US National Security Adviser Jake Sullivan told journalists Washington was preparing specific robust responses in the weeks ahead if they were required.

"Things we did not do in 2014 we are prepared to do now," he said, referring to Western responses to Russia's annexation of Crimea.

"There was a lot of give and take, there was no finger-wagging, but the president was crystal clear where the United States stands on all of these issues," he added.

The measures included economic sanctions and other actions such as additional troop deployments to Nato allies in the region and defence materiel for Ukraine.