Ukrainian President Petro Poroshenko and Russian President Vladimir Putin sat down for talks, meeting face-to-face for the first time since June, to discuss resolving the conflict pitting Kyiv against pro-Moscow separatist rebels.
The two were joined by the presidents of Belarus and Kazakhstan and three senior officials from the European Union, including EU foreign policy chief Catherine Ashton.
Meanwhile, footage posted on the Ukrainian government's "Anti-Terrorism Operation" Facebook page purported to show what it said were Russian soldiers captured on its territory. The video was posted only hours before the presidents of the two countries were due to meet in Minsk, Belarus.
Tuesday's video provided the strongest evidence yet to back up Kyiv's claims that Moscow is fueling the insurgency, sharply raising the stakes for the meeting between Poroshenko and Putin.
In opening remarks Tuesday in Minsk, Belarusian President Alexander Lukashenko urged both sides to "discard political ambitions and not to seek political dividend."
Lukashenko said talks were unlikely to bring any major breakthrough, but the meeting could be the start of a peace process.
The Ukrainian president was expected to face pressure to find a negotiated settlement - not a military victory - to the fighting that began in April. That was the option called for by German Chancellor Angela Merkel in a visit to Kiev last weekend.
The meeting represents a fresh diplomatic push to end five months of fighting in eastern Ukraine that has left over 2,000 people dead.
Before the face-to-face meeting, Poroshenko said the goal of his visit is to do everything possible to stop the bloodshed in eastern Ukraine and begin the process of finding a political compromise.
In early statements, Putin said the Ukraine crisis cannot be resolved through further escalationn of force or without launching a peace dialogue with separatists in Ukraine's eastern regions.
Ukraine's media on Tuesday aired footage purporting to show 10 Russian paratroopers, captured near Donetsk on Monday, confessing to entering Ukraine in armored convoys.
"We traveled here in columns not along the roads but across the fields," said one of the men who identified himself as Corporal Ivan Milchakov from the 331st parachute regiment, based in western Russia.
"I didn't even see when we crossed the border," Milchakov said.
Moscow has repeatedly denied any involvement in the rebellion in Ukraine and demands Kyiv halt its punishing offensive.
A Russian defense ministry source described the captured soldiers Tuesday 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.
Ukraine rejected that explanation. “This wasn't a mistake, but a special mission they were carrying out,” military spokesman Andriy Lysenko said in a televised briefing.
Ukrainian military spokesman Olekseyi Dmitrachkovskiy also said, “Yesterday, these people were questioned and they gave testimony that most of them knew they were going to Ukraine.”
U.S. National Security Adviser Susan Rice slammed Russia for "military incursions" into Ukraine using artillery, air defense systems, tanks and troops, that she said represented a "significant escalation" in the conflict.
Ashton said on Tuesday that her mission at the Ukraine crisis talks was to ensure the former Soviet republic can safeguard its territorial integrity.
Ashton said at the start of the high-level meeting that she wanted to “try and support the people of Ukraine to find peace and security, to ensure that they are able to enjoy territorial integrity, a future that is economically viable... and growing and good relations with the neighbors.”
Meanwhile, local authorities in the main rebel bastion of Donetsk, Ukraine, said three civilians were killed in shelling overnight as the army pummels insurgent fighters hunkered down there.
Lysenko also said separatists were attacking the southeastern border town of Novoazovsk “at this very minute” and Ukrainian forces had destroyed 12 armored infantry vehicles in the area.
The Ukrainian military said that 12 soldiers had been killed and 19 wounded in the past 24 hours.
At a frontline Ukrainian military position, soldiers said they battle daily with pro-Russian separatists located about 10 kilometers away.
A rocket-launcher site was destroyed in one of the frequent barrages of rebel fire, which comes every day, according to a young soldier named Oleg.
“You can't tell, it can be in 10 minutes, in 2 minutes or in 24 hours, or shelling all the time from artillery mortars or grad rockets," he said.
Fighting has intensified in the run-up to the key talks in Minsk with the rebels appearing to launch a counteroffensive after losing swathes of territory to a push by government forces.
Near the town of Debaltseve, Ukrainian national guards stopped a car when it tried to avoid a checkpoint. Inside the car, security forces found what they believed to be a drunk driver, machine guns and Russian passports.
Three accused separatists pulled from the vehicle are being investigated.
Poroshenko and Putin last met briefly in France at ceremonies to mark the 70th anniversary of the D-Day landings at the beginning of June.
The meeting in Minsk comes a day after Poroshenko dissolved parliament and called for early elections on October 26. In a televised statement, he said the vote is necessary in order to "cleanse" parliament.
Poroshenko said the last parliamentary election in 2012 was neither free nor fair. He said most lawmakers have lost the Ukrainian people's trust, noting there are "quite a few" members of parliament who support pro-Russian separatists in the east.
The U.S. has also condemned Russia for sending a convoy of 200 trucks full of purported humanitarian aid into Ukraine last week. The Kyiv government did not approve the shipment and called it a Russian invasion. It also said Russia did not wait for the Red Cross to complete its inspection.
Poroshenko's office said he told European Council President Herman Van Rompuy by telephone Monday that he is concerned about Russian plans to send another similar convoy into Ukraine.
Gabe Jaselow contributed to this report from Debaltseve, Ukraine. Some information for this report provided by Reuters, AFP and AP.