"The calibers banned by the Minsk agreements are being constantly used," he told TV Channel 112 Ukraine.

Read alsoOSCE sees over 30,000 individuals in military dress coming from Russia to Donbas"In the past day, there were 40 militant attacks with the use of 152mm and 122mm self-propelled artillery systems. The village of Shyrokyne [near the Ukrainian-controlled strategic port city of Mariupol] was attacked by a tank. We saw shooting earlier, but now no one of the Russian mercenaries cares and Grads and self-propelled artillery systems are used," he said.

Earlier, Ambassador of the United States Daniel B. Baer to the OSCE Permanent Council expressed concern about escalation in the Mariupol sector in Donbas, eastern Ukraine.

"We remain gravely concerned over the build-up of combined Russian-separatist forces outside Mariupol. Combined Russian-separatist forces blocked SMM [OSCE Special Monitoring Mission to Ukraine] monitors from accessing two different areas northeast of Mariupol on November 14. Given that the SMM has observed a link between access restrictions and ceasefire violations, we are deeply concerned that combined Russian-separatist forces may be planning more attacks against Mariupol or its environs," he said on November 17.

"Just two weeks ago, combined Russian-separatist forces launched an attack using multiple launch rocket systems on a suburb of Mariupol. We call on Russia and the separatists it backs to give OSCE monitors full and unfettered access to the area around Mariupol and immediately withdraw proscribed weapons," he added.