KIEV, July 13 – Russia-backed militants have steeply intensified shelling of Ukrainian army positions in the Donetsk and Luhansk regions, triggering concerns the confrontation may escalate and bury the Minsk peace deal.

Oleksandr Turchynov, the secretary of the National Security and Defense Council, traveled to the area of the conflict on Wednesday and said the militant forces used heavy weapons banned under the peace deal.

“The forces have significantly increased the number of attacks that are conducted with a defiant disregard for agreements on the withdrawal of heavy weapons from the line of contact,” Turchynov said in comments released by the council.

"The enemy uses 152-mm and 122-mm artillery systems that are prohibited under the Minsk agreement,” he said.

In many areas the Russian-led forces moved closer to the Ukrainian positions – in some cases as close as 300 meters down from 2,000 meters - and set up mortar and artillery systems to target the Ukrainian army.

Russia stepped up supplies of lethal weapons and ammunition to the militants that together with the increased shelling signals the separatist forces are preparing an offensive, Turchynov said.

"All this is a confirmation that the Russian General Staff is preparing an offensive operation,” Turchynov said.

The escalation of shelling the in the conflict zone comes days after NATO and Russia have failed to agree positions on how the conflict in parts of Ukraine’s Donetsk and Luhansk regions must be addressed.

Ukraine won promises of continued support at a NATO summit in Warsaw on Saturday.

NATO agreed during the two-day summit to boost its eastern flank in response to Russia's 2014 annexation of Crimea from Ukraine and Moscow's subsequent backing for rebels fighting Kiev troops in east Ukraine.

NATO Secretary-General Jens Stoltenberg said after the meeting that Russia must stop its "political, military and financial support for separatists" in east Ukraine.

The peace deal for the parts of Donetsk and Luhansk regions, negotiated in Minsk between Ukraine and Russia by Germany and France, has stalled for months. Paris and Berlin have now renewed efforts to implement it in full. (nr/ez)