Update | EU debates more sanctions as Russia 'flattens' Ukrainian town

Ukrainian President Petro Poroshenko said hundreds of foreign tanks were operating in his country, pleading for help from the European Union as it moved to slap tougher sanctions on the Kremlin.

"Ukraine now is a subject of foreign military aggression and terror," Poroshenko said in Brussels before a summit with leaders of the 28 EU member states. "Thousands of foreign troops and hundreds of foreign tanks are now on the territory of Ukraine."

EU leaders including German Chancellor Angela Merkel, British Prime Minister David Cameron and French President Francois Hollande were in Brussels to elect a president and foreign policy chief of the 28-nation bloc. They were scheduled to meet Poroshenko, who held talks yesterday with EU President Herman Van Rompuy and European Commission President Jose Barroso.

The summit comes as Ukraine's armed forces are retreating in some areas after Nato said Russia had deployed troops and advanced equipment in Ukraine. The allegation was dismissed by Russian Foreign Minister Sergei Lavrov, who said alliance satellite photos came from "computer games" and had been faked.

"We are in a very serious, I would say dramatic, situation," Barroso said at a news conference with Poroshenko. "We may see a situation that has reached a point of no return."

Hollande said EU leaders would agree to impose more sanctions on Russia at their talks.