The crisis in eastern Ukraine is "slipping out of control" and needsto be reigned in to avoid a military clash with Russia, Germany has warned.
Foreign Minister Frank Steinmeier made the remarks on the eve of an EU summit which will consider further sanctions against the Russian government.
Russia has denied claims by Nato that its forces illegally crossed into Ukraine to support separatists there.
Some 2,600 people have died in fighting between rebels and Ukrainian troops.
The conflict erupted in April when Russia's annexation of Crimea prompted rebels to take control of large parts of the eastern regions of Donetsk and Luhansk.
Russian President Vladimir Putin has blamed Ukraine for the crisis, comparing its siege of Donetsk and Luhansk to the siege of Leningrad by Nazi Germany in World War Two.
On Friday, Mr Steinmeier warned that the "already dangerous situation" in Ukraine had now entered "a whole new dimension".
"Our hopes that direct talks between [Ukraine and Russia] would contribute to de-escalating the situation have been disappointed," he said in Milan.
"The border infringements have intensified, and raised concerns that the situation is slipping out of control."