The Kremlin on Thursday rejected what it called "unfounded accusations" by the United States and NATO that it was not withdrawing its forces from near Russia's border with Ukraine, saying it takes time to wind down military exercises.
Moscow announced on Tuesday a partial force pullback, easing Western fears of a looming invasion of Ukraine, but the United States and NATO said on Wednesday the Russian military presence there was actually growing, not diminishing.
Kremlin spokesperson Dmitry Peskov told a news briefing that Russia's defence ministry had a clear timetable for the return of units to their permanent bases, reports Reuters.
"It's clear the grouping for the (military) exercises was built up over many weeks, and it is of course impossible to withdraw it in a single day. They can't just take off and fly away... it takes time," Peskov said.
"As always unfounded accusations," he added.
Russia has repeatedly denied any plan to invade Ukraine, despite massing - according to US estimates - some 150,000 troops near the border. Russia is also holding huge military exercises in Belarus that are set to run until Sunday.
Peskov said Moscow was seriously concerned about a flare-up in violence in the Donbass region of eastern Ukraine between Ukrainian government forces and pro-Russian separatists and it was monitoring the situation closely.
The rebels and Ukrainian forces traded accusations on Thursday that each had fired across the ceasefire line.
The conflict in the Donbass began in 2014 and has simmered since then despite numerous ceasefires.
Russia's military buildup has spurred Western fears that some kind of staged provocation in eastern Ukraine could serve as an excuse for a full-blown offensive.