Maas added that Russia will be needed to help resolve international tensions.

The statement came as German Chancellor Angela Merkel prepares to congratulate Putin on his re-election as Russia’s president following Sunday’s election.

Mass told reporters in Brussels on Monday that “the result of the election in Russia did not surprise us any more than the circumstances of this election”.

“We certainly cannot talk in all respects about a fair political contest as we know it,” he said, before talks with his European Union counterparts.   

The minister said it was “unacceptable” that the Russian election also took place in Crimea, which Russia annexed from Ukraine four years ago in breach of international law.

“In this respect, we assume that Russia will remain a difficult partner,” Maas added.   

“But Russia is also needed when it comes to resolving the major international conflicts and that is why we want to remain in dialogue,” the minister said.   

Russia is a key player in Ukraine, but also in the civil war in Syria and in the nuclear standoff on the Korean peninsula.   

“We also expect Russia to make constructive contributions, more so than has been the case in the recent past,” he said.   Maas said the ministers will discuss the situation in the Ukraine where the EU accuses Moscow of supporting a rebellion in the east.  

The foreign ministers' meeting will also focus on British allegations that Russia used a nerve agent to poison a former Russian spy in Britain, charges which Moscow denies.

Meanwhile, Chancellor Merkel will congratulate Putin on his re-election, in a message that will also raise “challenges” in their relations, her spokesman said.  

“I cannot pre-empt the content of the congratulatory message, but I believe that the message will also mention the challenges in Germany and Russia's relations,” Steffen Seibert, Merkel's spokesman, told reporters.   

Berlin and Moscow have “differences in opinion” on issues ranging from Russian politics to the conflicts in Ukraine and Syria, said Seibert.

“Nevertheless, the continuous contact with Russia's leadership is very important to us,” he stressed.