Dmytro Kuleba, Ukraine’s foreign minister, told reporters that Western governments should prepare a clear package of economic sanctions to be used immediately in the event of a Russian invasion.

He asked for increased defence and security support for his country, as well as government-to-government warnings to Russia about the consequences of any attack.

Ukraine estimates that there are some Russian 115,000 troops amassed near its borders, including forces in Russian-occupied Crimea.

“If Russia decides to undertake a military operation, things will literally be happening in the blink of an eye,” Mr Kuleba said. “The time frame in which to act is the coming months.”

Recep Tayyip Erdogan, the Turkish president and an ally of Russia, on Monday offered to mediate between Moscow and Kyiv to ease tensions. 

He told media he hoped that “this region does not become dominated by war”.

Turkey “would like to have a share in the solution of this by developing these talks both with Ukraine and with Mr Putin”, he said.

Kremlin spokesman Dmitry Peskov, however, was quick to reject the idea of Turkish mediation, insisting that Kyiv should speak with Russia-backed separatists directly.

Ukraine regards the separatists in its east as puppets of Moscow, and is opposed to direct engagement.

Mr Putin, who often describes Mr Erdogan as a personal friend, has not commented.