NATO Secretary-General Jens Stoltenberg said the alliance is seeing "more loss of life, a rise in cease-fire violence, obstruction of the monitors, and continued Russian support for the separatists" in eastern Ukraine, Censor.NET reports citing The Wall Street Journal.
"This is a disturbing trend in the wrong direction," he said Monday.
Mr. Stoltenberg added that Russia has continued to provide Ukrainian separatists with heavy weapons, artillery, training, and personnel. "That is also a blatant violation" of the agreement signed in mid-February, he said.
Russian authorities, who deny providing aid or troops to the rebels in Ukraine, agree the cease-fire is being routinely violated. But they blame the Ukrainian government in Kyiv, asserting that most civilian casualties have been on the separatist side.
"This is the answer to the question as to who is bombing, or is aiming, at whom," Russian Foreign Minister Sergei Lavrov said recently.
U.S. Deputy Secretary of State Antony Blinken last week said significant violence continues to flare in pockets, "perpetrated almost exclusively by the separatists and by the Russians who back them and indeed provide command-and-control.
"Every point of conflict is the result of the separatists trying to expand their territory, backed and supported by Russia," Mr. Blinken told reporters.
The deal was brokered by German Chancellor Angela Merkel, French President François Hollande and Russian President Vladimir Putin in Minsk, Belarus.
Beyond a halt to hostilities, which has killed some 6,000 people over the past year, the accord called for the withdrawal of heavy weapons from the battle zone, the pullout of foreign militaries, the release of hostages and similar measures to de-escalate the tension.
"It is an uneasy, imperfect implementation of the Minsk agreements right now," said Douglas Lute, the U.S. representative to NATO.
Western officials are also concerned by what they describe as a renewed Russian military buildup on the Ukrainian border in recent months.
"They have the capacity, the capability, to launch new attacks with very little warning time," Mr. Stoltenberg said. "But of course no one can say anything with certainty about their intention."
The NATO foreign ministers, including Secretary of State John Kerry, will tackle such issues at their meeting on Wednesday and Thursday. They will also discuss a range of other matters, from Islamic State to Afghanistan to NATO's new rapid-reaction force.
As shaky as the Minsk cease-fire might be, Mr. Lute argued that it is better than no deal at all.
"Having it in place, and judging ourselves against standards, is better than pre-Minsk, where there were no rules of the road, no standards against which to be judged," Mr. Lute said. "The fact is, there is a diplomatic process in place now which offers at least some promise."
The scrutiny of the cease-fire is part of the wider back-and-forth between Russia and the West at a time of heightened tensions. Partly due to an increased assertiveness by Russian aircraft, NATO recently reviewed its communication lines with the Russian military to ensure the two sides could talk quickly if a crisis or confrontation arose. Officials concluded the necessary channels were open.
"We have to make sure incidents, accidents, first of all don't happen, but if they do happen, they don't spiral out of control," Mr. Stoltenberg said.