The United States has warned that Russia could attack Ukraine at any point amid mounting tensions along the border.

White House Press Secretary Jen Psaki said at a news conference on Tuesday, "We are now at a stage where Russia could at any point launch an attack in Ukraine."

Western nations are calling for Russia to withdraw an estimated 100,000 troops amassed near the country's border with Ukraine.

Psaki said the US was informed that the Russian government was preparing to evacuate family members of Russian diplomats from Ukraine around late December to early January.

The US and Russian governments say US Secretary of State Antony Blinken and Russian Foreign Minister Sergey Lavrov talked on the phone on Tuesday.

Blinken stressed the importance of continuing a diplomatic path to de-escalate tensions over the Russian military buildup.

Lavrov said he expects a prompt written response to Russia's demand for assurances that NATO will not expand further. He also urged the US not to replicate speculation about alleged "Russian aggression."

Blinken and Lavrov agreed to hold face-to-face talks in Geneva on Friday. Blinken plans to visit Ukraine two days before that to meet President Volodymyr Zelenskyy and Foreign Minister Dmytro Kuleba.

He will also visit Germany to meet the country's foreign minister, Annalena Baerbock, on Thursday.