US President Joe Biden will call Ukraine's leader Volodymyr Zelensky Thursday in a show of support after warning Vladimir Putin of sanctions "like none he's ever seen" should Russian troops attack Ukraine.

The dramatic warning came a day after Biden and Putin talked for two hours by video link, and the US leader said his Russian counterpart got "the message."

After speaking to Zelensky, Biden will call nine NATO Eastern European countries, including Poland and the Baltic states, to discuss his summit with Putin, the White House said. 

"I made it very clear if in fact he invades Ukraine there will be severe consequences, severe consequences -- economic consequences like none he's ever seen or ever have been seen," Biden told reporters at the White House on Wednesday.

But he added that sending US troops to confront Russia was "not on the table." 

Zelensky has said it was "positive" the US and Russian leaders spoke directly. 

"I believe that Ukraine's victory lies in the fact that the United States has always supported Ukraine, our sovereignty and independence," the Ukrainian leader said after the Putin-Biden call. 

Western European countries added to the diplomatic pressure on the Kremlin following the Biden-Putin talks.

New German Chancellor Olaf Scholz warned of "consequences" for the Nord Stream 2 pipeline, a controversial Russian project to deliver natural gas to Germany. France's foreign ministry warned Russia would face "strategic and massive consequences."

US Secretary of State Antony Blinken said he had heard a similar message during talks with the president of the European Council, Charles Michel.

They "agreed on the need to impose swift and severe costs on Russia if it escalates its aggression in Ukraine," State Department spokesman Ned Price said.

Criminal inaction

Putin justified Russia's movement of up to 100,000 troops to the border of Ukraine over the past few weeks as a defensive measure amid fears in the Kremlin that ex-Soviet Ukraine is being pulled into NATO's sphere. 

The troop surge follows a similar build-up in the spring. 

On Wednesday, Putin conspicuously refused to say if he planned to invade Ukraine.

He said that simply watching NATO move closer to Russia would amount to "criminal inaction" and insisted Moscow has "the right to defend its security"

"We cannot but be concerned about the prospect of Ukraine's possible admission to NATO, because this will undoubtedly be followed by the deployment of appropriate military contingents, bases and weapons that threaten us," he said.

During the talks with Biden, the Russian leader has demanded that the West provide legal guarantees NATO will halt its eastward expansion. 

On Thursday, Moscow's foreign ministry said Russian diplomats had begun working on follow-ups in the wake the summit, without providing details. 

Ukraine's Western-leaning government wants to join the NATO military alliance but is nowhere close to being admitted. 

Russian troops already occupy Ukraine's Crimea peninsula and Russian-backed separatist forces have carved out a pro-Moscow territory covering a swath of eastern Ukraine. 

The conflict has killed more than 13,000 since erupting in 2014.  

New ceasefire talks 

On Wednesday, Ukraine held a new round of ceasefire talks, focusing on ending fighting, releasing detainees and reopening travel between regions held by Kiev and separatists.  

"There is a common understanding that the long-lasting ceasefire is a priority," OSCE Special Representative Mikko Kinnunen said after the talks, urging "further constructive work."

The OSCE said that while the number of ceasefire violations in the last two weeks was "lower" compared to previous weeks, the situation on the frontline was "still of concern". 

Zelensky called on the breakaway statelets to open checkpoints allowing people living in separatist-held regions to cross into territory controlled by Kiev. 

"Especially now, before the Christmas and New Year holidays, this is very important from the humanitarian point of view," Zelensky said Wednesday.

Biden said that in addition to economic measures, a new Russian attack on Ukraine would trigger a bolstered US military presence on the territory of existing NATO allies in eastern Europe. 

The United States works closely with the Ukrainian military and has committed more than $2.5 billion in security assistance to the country since 2014.