The presidents of Russia and Ukraine hold key talks today with little hopes for a breakthrough in the conflict pitting the former Soviet state against pro-Russian separatist rebels.
Kiev ratcheted up tensions by announcing hours ahead of the talks it had captured 10 Russian soldiers on its territory, while Washington accused Moscow of escalating the conflict with repeat military incursions.
Ukrainian President Petro Poroshenko and Russian leader Vladimir Putin are due to meet in Minsk alongside top EU officials and the leaders from Kazakhstan and Belarus, in a bid to defuse tensions that some fear could trigger direct hostilities between Russia and Ukraine.
US National Security Adviser Susan Rice slammed Moscow for "military incursions" into Ukraine using artillery, air defence systems, tanks and troops, representing a "significant escalation" in the conflict.
"Repeated Russian incursions into Ukraine unacceptable. Dangerous and inflammatory," she wrote on Twitter.
Kiev's security service said paratroopers from Russia's 98th airborne division were captured about 50 kilometres southeast of the main rebel stronghold of Donetsk.
Ukrainian media today aired footage purporting to show the captured Russian paratroopers confessing to entering Ukraine in armoured convoys.
"We travelled here in columns not along the roads but across the fields," says one of the men dressed in camouflage.
Kiev has long accused Moscow of stoking the separatist insurgency raging in its east, but this is the first time Ukrainian authorities have claimed to have captured soldiers from Russia's regular army.
"Officially, they are at exercises in various corners of Russia. In reality, they are participating in military aggression against Ukraine", Defence Minister Valeriy Geletey said on his Facebook page.
Moscow has repeatedly denied any involvement in the rebellion in Ukraine and demands Kiev halt its punishing offensive.
A Russian defence ministry source described the captured soldiers today as having crossed into Ukraine "by accident".
The soldiers had been "taking part in patrolling a section of the Russian-Ukrainian border; they crossed it most likely by accident, on an unequipped, unmarked section", Russian news agencies quoted the source as saying.
Foreign Minister Sergei Lavrov reacted earlier saying suggesting it was more "disinformation" about Russian activity.
On the ground there appeared no end in sight to the four months of conflict that has already claimed some 2,200 lives.
Local authorities in the main rebel bastion of Donetsk said three civilians were killed in shelling overnight as the army pummels insurgent fighters hunkered down there.
An AFP journalist reported the sound of heavy artillery fire to the west and south of Donetsk and saw Grad rockets fired by Ukrainian forces towards the town of Olenivka.
