Burkhalter will fly to Moscow on May 7th, the Kremlin said in a statement on Sunday  after President Vladimir Putin spoke by phone with German Chancellor Angela Merkel.
   
"Putin and Merkel stressed the importance of effective international action — especially by the OSCE — in reducing the tensions in Ukraine," Russia said in a statement.
   
Putin underlined the need to establish dialogue between the pro-Western leaders in Kiev and the pro-Russian separatists in eastern Ukraine, who control more than a dozen towns.

Russian Foreign Minister Sergei Lavrov earlier on Saturday asked his US counterpart John Kerry to press Ukraine to halt its military operation in the east of the ex-Soviet country, his ministry said.
   
"The minister called on the United States to use all of its influence to force the Kiev regime, which it looks out after and which has declared a war against its own people, to immediately halt military operations in the southeast, pull back its troops and free protesters," the Russian foreign ministry said.

And Lavrov, who also spoke with Burkhalter, pushed for a greater OSCE role in mediating the crisis in Ukraine, the ministry said.
   
"Sergei Lavrov strongly called for the use of the OSCE potential to influence Kiev with a view to cancelling a military operation against the population of Ukraine's southeastern regions," the ministry said in another statement.