KYIV, Ukraine -- At least 15 pro-Russian rebels were killed in clashes with government troops at a border crossing with Russia, an aide to the Ukrainian interior minister said Thursday.

Speaking on a television show late Thursday, Anton Herashchenko said Ukrainian border guards clashed earlier in the day with armed men who came from Russia in trucks and an infantry vehicle and tried to cross the border at the village of Marynivka in eastern Ukraine.

Herashenko said the attackers were supported by about a hundred rebels who came from the Ukrainian side of the border. Five Ukrainian troops were injured and 15 rebels were killed, and their bodies were taken to a nearby town, he said.

His account could not be confirmed independently.

Ukrainian government troops for weeks have been clashing with pro-Russian rebels who dismiss the Kyiv government as illegitimate and are now seeking independence.

Following the clash, Ukraine's government ordered the closing of parts of the border with Russia, including the Marynivka crossing, in an attempt to prevent armed men from infiltrating into its territory. The Russian Foreign Ministry said it was "outraged" by this move.

Candy magnate Petro Poroshenko, who is to be sworn in as Ukraine's next president on Saturday, has promised a comprehensive plan to put an end to the hostilities in the east as soon as he assumes office.

World leaders are gathering in Normandy on Friday for D-Day celebrations where Poroshenko and Russian President Vladimir Putin are expected to have some sort of interaction although an official meeting was not planned.