The North Atlantic Treaty Organization (NATO) says the Minsk ceasefire agreement has been violated frequently, accusing Russia of supporting pro-Moscow forces in eastern Ukraine.
"The ceasefire is violated again and again, and this is of great concern," NATO Secretary General Jens Stoltenberg said at a press conference following a meeting with the defense ministers of the Western military alliance about Ukraine on Wednesday.
"Russia supports the separatists ... with equipment, with weapons. They also mass troops along the Ukrainian border," Stoltenberg added.
Russia is yet to comment on the remarks but Moscow had previously denied involvement in the crisis in eastern Ukraine.
"We see many ceasefire violations over a long period of time. There are also many causalities. Ukrainian soldiers have lost their lives," the NATO chief said, referring to a recent report by the Organization for Security and Cooperation in Europe (OSCE).
OSCE international observers registered more than 200 blasts on Sunday and Monday in eastern Ukraine, as well as shelling, heavy machine gunfire and grenade attacks that annihilated buildings and left craters in the ground.
This comes as EU leaders are scheduled to decide on the extension of the sanctions against Russia over Ukraine’s crisis at the upcoming summit on June 28-29.
Ukraine’s eastern provinces of Donetsk and Lugansk have witnessed deadly clashes between pro-Moscow forces and the Ukrainian army since Kiev launched military operations later in April 2014 to crush pro-Moscow protests there.
The crisis has left more than 9,200 people dead and over 21,000 others injured, according to the United Nations.
In September 2014, the government in Kiev and the pro-Russians signed a ceasefire agreement in the Belarusian capital of Minsk in a bid to halt the clashes in Ukraine’s eastern regions.
The warring sides also inked another truce deal, dubbed Minsk II, in February 2015 under the supervision of Russia, Germany and France.
Since then, however, both parties have on numerous occasions accused each other of breaking the ceasefire.
Conflict erupted in eastern Ukraine after people in the country’s Black Sea peninsula of Crimea voted for reunification with Russia in March 2014. The West brands the development as Moscow’s annexation of the territory. The US and its allies in Europe also accuse Moscow of having a major hand in the crisis in eastern Ukraine, a charge that Moscow denies.