Ukrainian border guards are in Russia and have started to examine the contents of a huge convoy of trucks that Moscow says is carrying relief goods for civilians in war-torn eastern Ukraine, a border guard official said Friday.

The purpose of the procession of trucks, which abruptly changed course earlier this week, has been the subject of dispute between Russia and Ukraine.

The Ukrainian government has expressed fears that the mission is a camouflaged effort to smuggle supplies to pro-Russian rebels and has vowed to keep the convoy out.

Russia insists that it should be permitted to send aid to the conflict-battered region, many of whose residents are Russian speakers.

The Ukrainian government, whose forces have been fighting the pro-Russian rebel groups for months, has said any aid needs its approval and has to go through the Red Cross or the United Nations.

Serhay Astahov, a spokesman for the the Ukrainian border guard service, told CNN on Friday that border guards had started inspecting the trucks at a checkpoint on the Russian side of the border from Ukraine's Luhansk region.

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