German Foreign Minister Frank-Walter Steinmeier has stressed the importance of Ukraine's regaining control over its eastern border.

"Ukraine should regain control over its borders, which it has lost," he told reporters after talks with his Ukrainian President Petro Poroshenko in Kyiv on Tuesday.

Steinmeier said that it also depended on Russia's readiness to cooperate.

"We will be able to judge it better and deeper after we hear Russia's opinion about proposals on the expansion of the OSCE observation mission," he said.