Ukraine claimed on Monday to have captured 10 Russian paratroopers on its soil, a day after Kyiv said that an enemy armored column had crossed the Russian border in a bid to open a second front in the war for eastern Ukraine.

Kyiv's security forces posted a video on their Facebook page that purported to show the captured soldiers, who identified themselves and their unit. The authenticity of the video has not been independently verified.

In the footage, a man identifies himself as Ivan Milchakov and says that he's with a paratroop regiment based in the Russian town of Kostroma.

"I did not see where we crossed the border," Milchakov said. "They just told us we were going on a 70-kilometer march over three days."

"Everything is different here, not like they showed it on television," he continued. "We've come here as cannon fodder."

The alleged incident comes as Ukrainian President Petro Poroshenko and his Russian counterpart Vladimir Putin prepare to meet in neighboring Belarus about the conflict.

'Crossed by accident'

Meanwhile, the Russian Ria Novosti news agency reported that the paratroopers had accidentally strayed into Ukraine, quoting an unnamed Russian Defense Ministry source.

"The soldiers really did participate in a patrol of a section of the Russian-Ukrainian border, crossed it by accident on an unmarked section, and as far as we understand showed no resistance to the armed forces of Ukraine when they were detained," the source said.

But Ukrainian military spokesman Andriy Lysenko said the Russian soldiers were sent into Ukraine on a mission, without futher providing details.

"This wasn't a mistake, but a special mission they were carrying out," Lysenko said in a televised briefing.

Russian incursions?

Lysenko told the Reuters news agency that Russian Mi-24 helicopters had attacked a Ukrainian border post on Monday, killing four guards.

"Yesterday, during the day, at the border post of Krasnatalovka, Russian Mi-24 helicopters attacked Ukrainian border guards. As a result of the attack, four guards were killed, three were injured," Lysenko said.

Kyiv claimed on Monday that its forces had intercepted Russian troops, disguised as separatist fighters, who had crossed the border in an armored column. Ukraine claimed that the armored advance was stopped near the southeastern city of Novoazovsk.

Fighting reportedly continued near the city on Tuesday, which is located 10 kilometers (6 miles) from the Russian border. According to the Associated Press, smoke columns were seen rising from the outskirts of Novoazovsk amid reports by residents of a heavy artillery barrage.

US condemnation

The US ambassador to Ukraine, Geoffrey Pyatt, said that developments in Ukraine's southeast pointed to Russian involvement.

Meanwhile, White House National Security Advisor Susan Rice accused Moscow of making incursions in Ukraine.

slk/sb (AP, Reuters)