"Apakan said that the SMM has reported on civilian casualties and observed damage to civilian homes and infrastructure," the OSCE SMM wrote on Facebook.

He noted, in particular, that there had been damage to the water filtration plant in Yasynuvata, upon which thousands of people on both sides of the contact line depend for heating, electricity and water.

Read alsoMilitants fire Grads on Avdiyivka from residential areas in Donetsk (video)"Escalation in the area is of grave concern, with the civilian population greatly suffering. Violence on such a scale, involving the loss of life, is unacceptable and the protection of civilians must be paramount," the OSCE SMM quoted Apakan as saying said.

The Avdiyivka-Yasynuvata-Donetsk airport triangle has long been a focus of fighting. The latest developments – with the OSCE SMM recording thousands of ceasefire violations on a daily basis, including the use of proscribed weapons – constitute a serious deterioration and a violation of the Minsk agreements.

Read alsoRussian side to JCCC hinders emergency repair works in AvdiyivkaApakan called on the sides to immediately cease fire and withdraw such weapons beyond agreed lines. He urged the sides to prioritize the protection of the civilian population.

The Chief Monitor added it was imperative that the OSCE SMM be given immediate, safe and unhindered access to the affected area, in order to allow for verification of compliance with the sides' obligations on ceasefire and withdrawal of weapons.

As UNIAN reported earlier, the combined Russian-separatist troops have been shelling Ukrainian positions near Avdiyivka and residential areas there since January 29, 2016.