DONETSK, Russia — Hundreds of trucks from a bitterly disputed Russian aid convoy to rebel-held eastern Ukraine rolled back across the border into Russia on Saturday.

An Associated Press reporter counted 225 of the white tarp-covered trucks as they drove from Ukraine into a Russian border town called Donetsk, which bears the same name as the largest rebel-held city in Ukraine. A second AP reporter on the Ukrainian side was able to look inside about 40 of the tractor-trailers and confirmed they were empty.

One driver who declined to give his name said the rest of the 260-truck convoy was expected to return within hours to Russia. The state news agency RIA Novosti cited the Russian customs service as saying the trucks were moving in six groups.

The trucks had crossed Friday into Ukraine bound for Luhansk, another rebel-held city in eastern Ukraine hard-hit by weeks of fighting between Ukrainian forces and pro-Russian rebels. The Ukrainian government and Western countries denounced the move as a violation of Ukraine’s sovereignty and accused Russia of using the convoy to smuggle supplies and reinforcements to separatist fighters.

Russia said the trucks carried only food, water, generators and sleeping bags.

In a separate development, NATO said it has mounting evidence Russian troops are operating inside Ukraine and launching artillery attacks from Ukrainian soil. Russia also rejected that accusation.

It remained unclear Saturday what the Russian convoy had actually delivered.

The convoy’s entry caused Russia-Ukraine tensions to spike. Russia sent the trucks in Friday, saying it had lost patience and Luhansk was on the edge of a humanitarian catastrophe. Ukraine condemned it as a “direct invasion.”