Berlin is concerned over the concentration of military forces on the Russian-Ukrainian border, spokesman for the German Foreign Ministry Christopher Burger has said.

"We are observing Russian military activity with concern and are in close contact on this issue with our European and transatlantic partners. We believe that military escalation must be prevented," Burger told reporters in Berlin on Monday.

He recalled that a meeting of the foreign ministers of Germany, France and Ukraine will take place in Brussels on Monday.

"We are, of course, talking with Russia ... It is important not to exacerbate an already difficult situation," he said.