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The Kremlin says Russian President Vladimir Putin has spoken to German Chancellor Angela Merkel to explain Russia's decision to withdraw its military observers from a joint group monitoring the truce in eastern Ukraine.

Putin said the Russian move announced earlier this week had been prompted by "restrictions and provocations" by Ukrainian authorities that made it hard for Russian officers to perform their duties.

Ukraine has criticized Moscow's decision, saying it could fuel hostilities.

The Kremlin said Putin and Merkel agreed Thursday to consider possible steps to ensure the Russian monitors' return. It added that they also spoke in support of a planned prisoners' exchange and a truce for the holiday season.

Fighting between Ukrainian troops and Russia-backed separatists has killed more than 10,000 since April 2014.