International efforts to defuse the standoff over Ukraine intensified Monday, with French President Emmanuel Macron set to hold talks in Moscow and German Chancellor Olaf Scholz in Washington to coordinate policies as fears of a Russian invasion mount.

The concentration of an estimated 100,000 Russian troops near Ukraine has fuelled Western worries that it heralds a possible offensive.

White House national security adviser Jake Sullivan warned Sunday that Russia could invade Ukraine "any day," triggering a conflict that would come at an "enormous human cost."

Russia has denied any plans to attack its neighbour, but is urging the US and its allies to bar Ukraine and other ex-Soviet nations from joining NATO, halt weapons deployments there and roll back NATO forces from Eastern Europe. Washington and NATO have rejected the demands.

Macron, who is set to meet in the Kremlin with Russian President Vladimir Putin before visiting Ukraine Tuesday, said last week that his priority is "dialogue with Russia and de-escalation."

Before heading to Moscow, Macron had a call Sunday with US President Joe Biden.

They discussed "ongoing diplomatic and deterrence efforts in response to Russia's continued military build-up on Ukraine's borders, and affirmed their support for Ukraine's sovereignty and territorial integrity," the White House said in a statement.

The French presidency said Macron sought to ensure "good coordination" with Biden in the call.

"The security and sovereignty of Ukraine or any other European state cannot be a subject for compromise, while it is also legitimate for Russia to pose the question of its own security," Macron said in an interview with French newspaper Journal du Dimanche published on Sunday Putin's spokesman, Dmitry Peskov, described Macron's visit as "very important," but sought to temper expectations, telling reporters that "the situation is too complex to expect a decisive breakthrough after just one meeting."

He noted that "the atmosphere has remained tense," adding that the US. and its allies have continued to ignore Moscow's security demands.

Continuing the high-level diplomacy, German Chancellor Olaf Scholz is set to meet with Biden in Washington Monday for talks also expected to focus on the Ukrainian standoff. Scholz is set to travel to Kyiv and Moscow on February 14-15.

National Security Adviser Sullivan, who spoke in a round of appearances on Sunday talk shows reiterated that the Russian Nord Stream 2 gas pipeline to Germany "will not move forward" if Russia attacks Ukraine.

Biden and Scholz are expected to address the pipeline during their White House talk, which will mark their first face-to-face since Scholz became the head of the German government nearly two months ago.

Ahead of the visit, the White House sought to downplay Germany's refusal to supply lethal weapons to Ukraine, bolster its troop presence in eastern Europe or spell out which sanctions it would support against Russia - moves that have drawn criticism abroad and inside Germany.

White House officials, who briefed reporters ahead of the meeting on the condition of anonymity. noted that Germany has been a top contributor of non-military aid to Ukraine and has been supportive of the US decision to bolster its troop presence in Poland and Romania to demonstrate its commitment to NATO.

On Sunday, German Defence Minister Christine Lambrecht raised the possibility that the country could send more troops to Lithuania to reinforce its presence on NATO's eastern flank.

Biden has ordered additional US troops deployed to Poland, Romania and Germany, and a few dozen elite US troops and equipment were seen landing Sunday in south-eastern Poland near the border with Ukraine with hundreds more infantry troops of the 82nd Airborne Division set to arrive.

In 2015, France and Germany helped broker a peace deal for eastern Ukraine in a bid to end the hostilities between Ukrainian forces and Russia-backed separatists that erupted the previous year following the Russian annexation of Ukraine's Crimean Peninsula.

The agreement signed in the Belarusian capital, Minsk, helped stop large-scale fighting, but efforts at a political settlement have stalled and frequent skirmishes have continued along the tense line of contact in Ukraine's eastern industrial heartland called Donbas.

The leaders of Russia, Ukraine, France and Germany last met in Paris in December 2019 in the so-called Normandy format summit, but they failed to resolve main conflicting issues.

Amid the tensions over the Russian military buildup, presidential advisers from the four countries held talks in Paris on January 26 this year, but they didn't make any visible progress and agreed to meet again in Berlin in two weeks.

Ukrainian President Volodymyr Zelenskyy has pushed for another four-way Normandy summit, but the Kremlin said a meeting of leaders would only make sense if the parties agree on the next steps to give a special status to the rebel east.

Putin and his officials have urged France, Germany and other Western allies to encourage Ukraine to fulfil its obligations under the 2015 agreement, which envisaged a broad autonomy for the rebel east and a sweeping amnesty for the separatists.

The agreement stipulated that only after those conditions are met would Ukraine be able to restore control of its border with Russia in rebel regions.

The Minsk deal was seen as a betrayal of national interests by many in Ukraine and its implementation has stalled. Amid the latest tensions, Ukrainian authorities have strongly warned the West against pressuring Ukraine to implement the agreement.

Last week, Oleksiy Danilov, the secretary of Ukraine's National Security and Defence Council, told The Associated Press that an attempt by Ukraine to fulfil the Minsk deal could trigger internal unrest that would play into Moscow's hand.