Poroshenko's website said he had spoken to Herman Van Rompuy, President of the European Council, after intensified fighting in the east, in which Kiev has alleged Russian involvement in an air strike on a residential area and the downing of a military transport plane.
Poroshenko informed Van Rompuy of new evidence of rebel fighters crossing into Ukraine from Russia along with heavy military equipment and arms, his website said.
He had called on the EU "to demonstrate a strong position of action by the European Union to support Ukraine", it said.
Diplomats in Brussels say EU leaders are likely to give the go-ahead on Wednesday to new sanctions, though they may fall short of the far-reaching economic measures sought by the United States and by some of the more hawkish members of the EU, including Poland and the Baltic states.
Ukraine has accused Russia repeatedly of turning a blind eye to Russian fighters crossing the long shared border to team up with rebels, often with Russian weapons and military equipment. Moscow denies this.
But the war of words has grown more shrill since a shell struck a Russian town across the border last Sunday, killing a Russian man. Moscow said the shell had been fired by Ukrainian government forces, though Kiev denies this, blaming it on rebels out to discredit government forces.
Eleven people were said by local health authorities to have been killed on Tuesday in an air strike on the Ukrainian town of Snizhne, 20 km (12 miles) from the border.
Kiev denied rebel charges that the strike had been carried out by a Ukrainian warplane and said it was the work of an "unknown" plane - apparently an accusation against Russia, since the rebels have not used aircraft in the conflict.
Kiev has also said that a missile that brought down an An-26 military transporter was probably fired from Russian territory. Kiev says it has found four survivors from the eight people who were on board, that two others are being held by rebels, and that it does not know the fate of the remaining two.
Since the Kiev government launched its "anti-terrorist" operations in mid-April, a total of 258 Ukrainian servicemen have been killed, and nearly 1,000 injured, the military says. Hundreds of civilians and rebels have also died.
Violence erupted in Ukraine's Russian-speaking east after a pro-Europe revolt in Kiev that ousted a Moscow-backed president in February and led to Russia's annexation of Crimea, causing the biggest Russia-West crisis since the Cold War.