With a six-month peace deal in danger of falling apart, Russian Foreign Minister Sergei Lavrov called on Germany and France Wednesday to pressure Ukraine to adhere to the treaty. Above, firefighters work on top of a house that locals say was recently damaged by shelling, in Donetsk, Aug. 12, 2015. Reuters/Alexander Ermochenko

German and French leaders should press Ukraine harder to implement the peace plan in eastern Ukraine that was signed in February, Russian Foreign Minister Sergei Lavrov said Wednesday. He spoke from Crimea, territory that Russia annexed from Ukraine in 2014, following reports that Russian-backed rebels were building up their "combat readiness" and only a week after a rebel official warned of "a big war" if the peace plan fell apart.

Each side blames the other for violating the ceasefire, brokered by France and Germany in February and signed in Minsk, Belarus. Ukraine's government says Russian-backed rebels in the east of the country are responsible, while Russia maintains that Kiev has failed to hold up certain aspects of the deal or hold direct talks with rebel groups.

Ukraine President Petro Poroshenko is scheduled to meet next Monday with German Chancellor Angela Merkel and French President François Hollande in Berlin. "It is necessary in our view to mount additional pressure on Kiev to convince them that they have to implement the agreements and obligations agreed in Minsk," Lavrov said, Reuters reported.

An official with a pro-Russian rebel group, which calls itself the Luhansk People's Republic, said Friday that Ukrainian forces were using lethal weapons from Poland and Italy. Kiev denied the claim, with Olexandr Turchynov, head of Ukraine's National Security and Defense Council, saying, "Until now, supplies of lethal weapons and modern military technologies are blocked, and there is only one way out for us -- to rely exclusively on own capacities and on own potential." Ukrainian officials also say Russian-backed forces have been shelling "around the clock using large-caliber artillery and multiple launch rocket systems, prohibited by the [peace agreements]."

As the dispute continues, Russia, at least, is pressing other countries to take steps. "We expect that on Aug. 24 ... Germany and France, who are the guarantors of the implementation of the Minsk agreement, will do everything to ensure it is carried out in full," Lavrov said.