"We will judge Russia and President Putin on their statements that the unity of Ukraine cannot be called into question," Steinmeier said in a Twitter message.
Russia said it would back the results of elections in the separatist areas of Luhansk and Dontesk in which two rebel leaders are set to win.
The polls have been condemned by the EU and United States as going against the Minsk agreement which was supposed to put Ukraine on the path to peace.
Steinmeier added the elections had "gone against the letter and the spirit of the Minsk agreement".
Federica Mogherini, the EU's new foreign policy boss, described the polls as "a new obstacle on the path towards peace".
Ukraine's President Petro Poroschenko called them a "farce".
But Russia said it would respect the "will of the people" in the elections.
Alexander Zakharchenko is set to win in Donetsk and rebel leader Igor Plotnisky will win in Luhansk.
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