Moscow said on Monday that US-led military exercises in western Ukraine that began this week may have "explosive" consequences and threaten to derail the peace process in the separatist east.

"The military drills involving NATO members and Ukraine's army that started in Lviv region under US command are a clear demonstration of NATO's provocative policy to unequivocally support the policies of current Kiev authorities in eastern Ukraine," the foreign ministry said in a statement.

Ukrainian and US troops on Monday launched fresh drills involving 1,800 soldiers from 18 countries, meant to bolster the morale of the armed forces amid an ongoing 15-month conflict with pro-Russian separatists.

Russia responded mere hours after the drills kicked off near Ukraine's border with Poland.

"Not only is NATO not ready to recognise the wrongness and possible explosive consequences of holding such drills but it is considerably increasing their scope," it said.

"These actions... may threaten to disrupt the visible progress in the peace process concerning the deep internal crisis in Ukraine," it said.

Kiev has been locked in a conflict since April 2014 with pro-Moscow rebels in parts of the Donetsk and Lugansk regions, accusing Russia of funnelling in troops and resources to sustain the insurgency -- charges Moscow denies.

A peace accord was struck in the Belarussian capital Minsk in February, but deadly clashes continue despite the truce.