The presidents of Russia and Ukraine held the first bilateral talks since the February revolution in Ukraine, hours after Kiev stated it had captured 10 Russian soldiers on its territory.
Vladimir Putin and Petro Poroshenko held one-on-one talks late on Tuesday in the Belarusian capital of Minsk, after earlier meeting the presidents of Belarus and Kazakhstan and three senior officials from the European Union.
The meeting came as Ukraine said its forces had captured the Russian soldiers in eastern Ukraine and the shelling spread to a new front in the far southeast.
The Facebook page for the Ukraine's anti-rebel operation, which includes the military, the national guard and interior ministry forces, said on Tuesday that the soldiers were from a Russian paratrooper division and were captured on Monday in the area of Amvrosiivka, near the Russian border in the Donetsk region.
Ukraine has repeatedly accused Russia of supporting and arming the rebels, which Russia denies. Russia said on Tuesday that the soldiers had strayed into Ukrainian territory.
"The fate of peace and the fate of Europe are being decided in Minsk today," Poroshenko said as the talks began.
Speaking from Minsk, Al Jazeera's Rory Challands said Poroshenko proposed an Autumn peace conference and said it was in Ukraine's interest to wrap the war up ahead of the coming winter.
"At the moment Ukraine is making gains against the separatists in the east but the longer the conflict goes on the more powerful Moscow becomes.
"Firstly Russia can continue to support separatists and resupply them with weapons, and secondly as winter approaches and the weather gets colder there will be a serious problem as Ukraine currently gets no gas from Russia.
"Moscow will become a much more powerful actor in negotiations if this is not sorted out."
The Ukrainian president said the purpose of his visit was to start the process of searching for a political compromise and promised that the interests of Russian-speaking eastern Ukraine would be taken into account.
Al Jazeera's correspondent said Putin struck a more "combative stance and threatened more sanctions unless Ukraine changed its tone".