BRUSSELS, June 13 - Russia continues to keep its troops on Ukrainian territories controlled by separatists in eastern parts of the country, NATO Secretary General Jens Stoltenberg said Monday.

"Russia has a particular responsibility because it continues to support the separatists in Donbas,” Stoltenberg said, Ukrayinska Pravda reported. “We see Russian troops in the east of Ukraine.”

The comments come amid increasing violations of the ceasefire agreements and deteriorating violence in the region and as European leaders are soon to decide on whether to extend economic sanctions imposed against Moscow.

The comments come less than a month after President Petro Poroshenko urged Russia to stop massive supplies of lethal weapons to separatist enclaves and withdraw its troops immediately from Ukraine.

Russia keeps about 7,000 of its troops in parts of Donetsk and Luhansk reinforcing a 25,000-strong army of the separatist enclaves that mostly consists of Russian mercenaries, according to Ukrainian military intelligence.

Russia recently increased supplies of lethal weapons and ammunitions by railroad to the key separatist regions, the intelligence agency reported.

Russia persistently denies presence of its troops in Ukraine, and says it only supplies humanitarian aid to the enclaves.

Stoltenberg’s comments come a week after a Reuters reported that Russia was building a new military base in the Russian town of Klintsy 50-km from Ukraine, with large numbers of newly-arrived servicemen and military vehicles.

The apparent construction of the army base is the latest evidence of Russia bolstering its military capabilities in the region in an effort to counter NATO’s increased military exercises and deployments in eastern Europe in response to Russian intervention in Ukraine.

This week, NATO countries began a 10-day military exercise in Poland, the largest in eastern Europe since the end of the Cold War. The exercise involves 31,000 troops and thousands of military vehicles from 24 different member countries.

In May, Russian officials announced that the country would establish three new military divisions in the face of proposed NATO buildup in the Baltics. The divisions would reportedly each include about 10,000 soldiers. (nr/ez)