Diplomats from Russia and the US are to hold crucial talks as a weeks-long standoff over Ukraine teeters on the cusp of a pivotal and potentially violent phase, with rising concerns that Europe may again be beset by war.

Intelligence services in Ukraine claimed to have evidence that Russia was secretly moving weapons and oil into eastern Ukraine.

The US secretary of state, Antony Blinken, and Russia’s foreign minister, Sergey Lavrov, will meet in Geneva – once a key cold war crossroads – in an attempt to avert a possible Russian invasion of Ukraine amid Moscow’s demands for concessions from Nato over its relationship with the former Soviet republic.

On Friday morning, Russia appeared to toughen its stance ahead of the day’s talks. Its foreign ministry said Moscow was seeking guarantees from the west that included provisions requiring Nato forces to leave Romania and Bulgaria, countries that joined in 2004. That demand underscores the extent to which Vladimir Putin is seeking to recreate the Soviet Union’s old sphere of influence.