Washington DC - Russia and the US accused one another of heightening tensions in Ukraine on Saturday, but also left the door open for further diplomacy, despite weeks of inconclusive talks.

The US and its NATO allies charge that Russia is preparing to attack Ukraine, an accusation that Russia denies. However, Russia has also taken advantage of the tensions to demand that NATO restrict activities in Eastern Europe and promise to add no past Soviet republics as new members. It has also massed more than 100,000 troops on Ukraine's borders.

Meanwhile, Kyiv is preparing for the worst, but also making appeals for the West to tone down the rhetoric, even as country after country urges its citizens to get out of Ukraine.

Saturday was tinged with another round of telephone diplomacy, perhaps most importantly with about an hour of talks between US President Joe Biden and Russian President Vladimir Putin.

Joe Biden Biden sours MAGA Republicans by beating Trump's record for judge appointments

The US is ready to engage in diplomacy with Russia about the situation in Ukraine, but is "equally prepared for other scenarios," Biden told Putin, according to a White House statement.

He also told Putin that the US and its allies would "respond decisively and impose swift and severe costs on Russia" in the event of a Russian invasion into Ukraine.

But Putin countered with anger at the US spreading reports that it is planning a Ukrainian invasion and instead pointed to the dangers that Western military support for Ukraine poses. Putin argued that Ukraine is trying to undo the peace accords that have maintained some calm, notwithstanding ongoing fighting between separatist groups in Ukraine's east and government forces.

"We can state that the conversation was rather balanced and business-like," Kremlin aide Yury Ushakov told the Itar-TASS news agency, adding that the two have agreed to maintain contacts.

According to Itar-TASS, the Kremlin argued that the current situation is creating a scenario in which Ukrainian forces might launch a provocation.

Russia also it will soon provide a reaction to US and NATO answers handed over recently in response to the Kremlin's call for security guarantees.

Putin took a similar line in a phone call with French President Emmanuel Macron, blasting "provocative speculation" about Russian attack plans and decrying the "large-scale pumping of cutting-edge weapons into that country and the creation of conditions for potential aggressive actions by [the] Ukrainian military."

Donald Trump Trump threatens Republican congressman with a primary challenge for refusing to raise debt ceiling

Meanwhile, Ukrainian President Volodymyr Zelensky told journalists on Saturday that his government had no information about a possible invasion aside from increasingly alarmist claims made by the US. He added that Ukrainian forces were nonetheless prepared for war.

On Friday, the US government said that it considers a Russian incursion into Ukraine possible before the close of the Winter Olympics in China on February 20.

In response to the tensions, NATO countries have deployed troops and equipment to fellow member states that share a border with Ukraine. Those have included the stationing of US troops in Romania and Poland.

A number of countries, including Russia, have advised their citizens to leave Ukraine.

Russian Foreign Ministry spokesperson Maria Zakharova justified the new guidance by pointing to "possible provocations by the Kyiv regime or third states."

Westerners in Ukraine were also urged to leave as soon as possible. Such warnings have been coming for weeks, but grew more urgent on Friday when Britain and the US told citizens to leave immediately. The call has since been repeated by scores of other countries.