Ukraine says Russian military vehicles crossed the border in southeastern Ukraine on Monday.
Correspondent Karoun Demirjian tells our Newscast unit that the accusations from the Ukrainian military come just as Russia announced it was sending another aid convoy into Ukraine.
Reporting from Moscow, Karoun filed this report:
"A Ukrainian defense spokesman says a group of Russian tanks and military vehicles have crossed into the far southeastern corner of the country, potentially opening up a new front in the government's ongoing conflict with pro-Russian separatists.
"It is the latest charge from Ukraine that Russia has been helping separatists fighting against government troops in the eastern part of the country.
"Russia's foreign minister denied having any knowledge of the incident Monday. But he announced that Russia would send a second aid convoy to eastern Ukraine sometime this week.
"Last Friday, Russia sent a shipment of humanitarian goods into eastern Ukraine without the government's permission."
The BBC reports that Ukraine was worried that the first convoy also included military help for the pro-Russian rebels.
The news service adds that Ukraine says today's column included armored personnel carriers and 10 tanks.
"Ukraine's military said border guards had halted the column about 5km (3 miles) north-east of Novoazovsk, which is about 10km from the frontier in the far south-east of Ukraine," the BBC reported. "Heavy clashes were reported at the village of Markyne."