Moscow announced Monday it would pull its officers from a joint Russia-Ukraine centre tasked with monitoring the implementation of a brittle ceasefire as Kiev slammed the "unprecedented" move as a provocation.
The latest spike in tensions came as Kiev said that three Ukrainian soldiers had been killed in fighting in the east of the ex-Soviet country.
In September 2014, Ukraine and Russia established a "joint centre for control and coordination" tasked with monitoring compliance with the ceasefire regime.
The Russian foreign ministry said Russian members of the joint monitoring centre, which is based in government-controlled territory near the rebel stronghold of Donetsk, would leave on Tuesday.
Russia accused Ukraine of preventing its officers from carrying out their duties including speaking to the local population.
"In such conditions the further work of representatives of the Russian armed forces in the Joint Center for Control and Coordination has become impossible," the foreign minister said in a statement.
Moscow added it had already notified its foreign partners and stressed that responsibility for the possible consequences would rest with Ukraine.
In Kiev, the Ukranian foreign ministry slammed the move, saying it was a new blow to a Western-brokered deal to end the conflict.
"We see this unprecedented step of Russia as a new provocation which considerably undermines the Minsk agreements," the foreign ministry said.
The ministry called it a new Moscow attempt to force Ukraine to begin direct negotiations with Kremlin-backed rebels.
The Ukrainian military fears Moscow's decision to quit the group could escalate the conflict.
"The enemy can resort to aggressive offensive actions," the Ukrainian army said in a statement.
On Monday, the Kiev military said three soldiers had died in clashes near the village of Zaitseve some 50 kilometres (30 miles) northeast of the rebels' stronghold of Donetsk.
It accused insurgents of using heavy weapons including large-calibre mortars, which are banned by ceasefire agreements.
The war in the east of the former Soviet republic broke out in April 2014, after Russia annexed Crimea the previous month, and has claimed more than 10,000 lives.
A series of periodic truce deals have helped lower the level of violence but not fully end the bloodshed.
Ukraine and its Western allies accuse Russia of funnelling troops and arms across the border.
Moscow has denied the claims despite overwhelming evidence that it has been involved in the fighting and its explicit political support for the rebels.