Leaders of France, Germany, Italy, UK and US express "determination" during a phone call that Ukraine's sovereignty should be respected.
Leaders of the United States, Germany, Italy, France, and Britain have emphasised the need to provide a united front in the face of soaring tensions between Russia and their ally Ukraine.
A spokesperson for British Prime Minister Boris Johnson on Monday said the prime minister spoke to US President Joe Biden, Italian Prime Minister Mario Draghi, French President Emmanuel Macron, and German Chancellor Angela Merkel about Ukraine.
"The leaders called on Russia to de-escalate tensions and reaffirmed their staunch support for Ukraine's territorial integrity," the UK PM spokesperson said.
The leaders also "expressed their commitment to act to maintain peace and security in Europe", the office of French President Macron said following the call.
Earlier, Ned Price, a US State Department spokesperson said if Russia chooses to aggress militarily upon Ukraine "we and our allies would be prepared to act, we would be prepared to act resolutely."
READ MORE: Why Ukraine matters to Russia so much
Ukraine president hails military
Ukrainian and Western officials are worried that the Russian military concentration near the border with Ukraine could herald plans by the Kremlin to attack its neighbour, a concern that is expected to dominate a call on Tuesday between Presidents Vladimir Putin and Joe Biden.
Meanwhile, Ukrainian President Volodymyr Zelenskyy praised the country's army as a "highly capable and highly organised force that is confident in its potential and is able to derail any expansionist plans by the enemy."
"Ukrainian servicemen are continuing to perform their most important mission — to protect the freedom and sovereignty of the state from the Russian aggressor," said Zelenskyy, who donned combat fatigues on a visit to troops near the area of a separatist conflict in the country's east.
Thousands of Russian troops at edgy frontier
The conflict with Russia-backed rebels in Ukraine's eastern industrial heartland erupted weeks after Moscow’s 2014 annexation of the Crimean Peninsula. The fighting has killed more than 14,000 people, and efforts to negotiate a settlement have stalled.
US intelligence officials have determined that Russia has massed about 70,000 troops near its border with Ukraine and has begun planning for a possible invasion as soon as early next year.
Moscow has denied hatching plans to attack Ukraine and rejected the Western concerns as part of efforts to smear Russia.
At the same time, Putin has urged the West to provide guarantees that would exclude Ukraine from joining NATO and the deployment of the alliance's weapons on its territory.