MOSCOW (AP) — Separatist rebels in eastern Ukraine on Friday accused government forces of shelling residential areas under their control with heavy artillery, while Ukrainian forces said the rebels were violating the cease-fire.

The rebel mouthpiece Donetsk News Agency said Ukrainian forces used Grad multiple rocket launchers Thursday night and Friday morning north of Donetsk. Under the Sept. 1 cease-fire, which has largely held, heavy weaponry was supposed to have been withdrawn weeks ago.

The uptick in fighting came as the foreign ministers of Russia, Ukraine, France and Germany met in Berlin to discuss progress in implementing the peace deal reached in Minsk in February for the conflict, which has claimed more than 8,000 lives since April 2014.

German Foreign Minister Frank-Walter Steinmeier said the ministers agreed to press forward with the effort to ensure that heavy weapons are withdrawn.

"It ought to be possible to conclude the withdrawal of heavy weapons by the end of November or the beginning of December," he said.

The ministers in Berlin also agreed there should be a deal by the end of this month on arrangements for demining, so experts can start removing mines before winter sets in, Steinmeier said.

He added that they expressed their dissatisfaction with a continuing lack of access for humanitarian organizations to rebel-held eastern Ukraine.

"No one is denying the difficulties and obstacles that we still face on the way to a political solution, but my impression here was that the participants are working to actually overcome these obstacles," he said.