MOSCOW (REUTERS) - Russian President Vladimir Putin told German Chancellor Angela Merkel on Sunday that the referendum in Ukraine's Crimea complied with international law, the Kremlin said in a statement.

Mr Putin promised to respect Crimeans' decision, the Kremlin added, as people cast their votes on whether to break away from Ukraine and join Russia.

The statement said Mr Putin also used his phone call with Ms Merkel to also express his concerns about an escalation of tensions he said were caused by radical groups in the southeastern regions of Ukraine in "connivance with Kiev's authorities".

"Vladimir Vladimirovich Putin drew attention to the fact that the will of the population of the peninsula is being implemented in full compliance with international law," the statement said.