Russia sent dozens of aid trucks into rebel-held eastern Ukraine on Friday without Kiev's approval, saying its patience had worn out with the Ukrainian government's stalling tactics. Ukraine called the move a "direct invasion."

The unilateral move sharply raised the stakes in eastern Ukraine, for any attack on the convoy could draw the Russian military directly into the conflict between the Ukrainian government in Kiev and separatist rebels in the east. Ukraine has long accused Russia of supporting and arming the rebels, a charge Russia denies.

The white-tarped semis said to be carrying food, water, generators and sleeping bags are intended to help civilians in the city of Luhansk, where government forces are besieging pro-Russian separatists. The city only 20 kilometers (12 miles) from the Russian border has seen weeks of heavy shelling that has cut off power, water and phone lines and has left food supplies scarce.

In the past few days, Ukraine says its troops have recaptured significant parts of Luhansk, the second-largest rebel-held city, and suspicions are running high that Moscow's humanitarian operation may instead be aimed at halting Kiev's military momentum. Fierce fighting has been reported this week both around Luhansk and the largest rebel-held city, Donetsk, with dozens of casualties.

Four troops were killed and 23 wounded in the past 24 hours, the government reported at noon Friday.

The International Committee of the Red Cross, which had planned to escort the Russian aid convoy to assuage fears that it would be used as a cover for a Russian invasion, said it had not received enough security guarantees to do so Friday.

Ukrainian security service chief Valentyn Nalyvaichenko on Friday called the arrival of the convoy a "direct invasion."

"This is a direct invasion done under the cover of the Red Cross for the first time ever," Nalyvaichenko told reporters in the Ukrainian capital, Kiev. "These are military men who have been trained to carry cargo, trained to drive combat vehicles, tanks and artillery."

He asserted that the half-empty aid trucks would be used to transport weapons to rebels and spirit away the bodies of Russian fighters killed in eastern Ukraine.

He promised, however, that Ukraine will not shell the convoy.

AP journalists heard the contents of many aid trucks rattling and sliding around on the country road, confirming that many vehicles were only partially loaded.

Ukraine had authorized the entrance of a few dozen trucks, but the number of Russian vehicles entering the country through a rebel-held border point Friday was clearly way beyond that amount.