AVDIIVKA, Ukraine — International monitors on Friday strongly urged the warring sides in eastern Ukraine to silence their guns as heavy artillery and rocket barrages continued to pummel residential areas.

At least 33 people including civilians have been killed and several dozen injured in fighting this week in eastern Ukraine between government forces and Russia-backed separatist rebels – the worst violence in the region since 2015.

The death toll in the fighting that began in April 2014 has now exceeded 9,800, according to U.N. figures and a tally of recent fighting.

“Unacceptable! … Sides have to stop fighting!” the monitoring mission of the Organization for Security and Cooperation In Europe said on its Facebook page.

While the warring sides have regularly exchanged gunfire despite a February 2015 peace deal brokered by France and Germany, this week has seen a sharp spike in hostilities. Fighting has raged around the government-controlled industrial town of Avdiivka, just north of the main rebel stronghold of Donetsk, catching residential areas in the crossfire.

“We have seen on both sides an incredible amount of cease-fire violations,” said Alexander Hug, deputy head of the OSCE’s monitoring mission.

Each side blamed the other for the upsurge of violence, but the Ukrainian military says its troops have gained some ground.