Russian Foreign Minister Sergei Lavrov said that he would call for an immediate ceasefire in eastern Ukraine during talks with his counterparts from Ukraine, France and Germany, in Berlin on Wednesday. Lavrov’s statement follows Ukraine’s claim on Tuesday that Russian troops had attacked its forces in the country’s east where pro-Moscow rebels have waged a months-long offensive.

Although a ceasefire agreement was reached in September, it has been violated frequently partly because a separation line agreed between the Ukrainian government and pro-Russian rebels did not account for the groups’ actual positions in the region, Lavrov said, at a news conference on Wednesday, according to Reuters.

Lavrov stated that Wednesday’s peace talks among officials from the four nations will focus on withdrawing heavy weapons from a redrawn frontline in eastern Ukraine, in an effort to end the recent escalation of fighting between Kiev's forces and separatists in the Donetsk and Luhansk regions. He also stated that Russian President Vladimir Putin had written a letter to the Ukrainian government, proposing the use of the original separation line to conduct the withdrawal of weapons, the Associated Press (AP) reported.

Lavrov’s statement comes after Kiev accused Russian forces of attacking its troops in eastern Ukraine on Tuesday in what is considered to be one of the most daring assertions by Ukraine of the Russian military's direct involvement in the conflict since the fighting began over nine months ago, Reuters reported.

“In spite of preliminary agreements, Ukrainian military units were attacked in the north of the anti-terrorist operational zone by regular military formations of the armed forces of Russia,” Reuters quoted Andriy Lysenko, a spokesperson for Kiev, as saying.

However, Russia has denied that any of its regular forces are deployed in Ukraine. According to Lavrov, both Ukraine and the West have failed to provide proof to support their claims about Moscow’s involvement in the fighting in eastern Ukraine, which has killed more than 4,700 people since April last year, AP reported.

While Ukraine blames Russia for aiding the rebels, the Kremlin said Tuesday that increased military activity by Ukraine's forces could be a hurdle in arranging the four-way summit. Meanwhile, the West has claimed that efforts to bring the four nations together have been hampered by Moscow’s failure to enforce the ceasefire agreement.