The first few dozen Russian trucks supposed to be carrying humanitarian aid to civilians in the rebel-controlled city of Luhansk, Ukraine, crossed the border Friday without a Red Cross escort or permission from the Kiev government.
Ukraine said the entrance Friday of the trucks is a clear violation of international law, and one security official called it a "direct invasion," according to The Associated Press.
Hundreds of trucks have been stuck at the Russian border for a week. Ukraine had initially resisted allowing the convoy into the country amid skepticism about the operation, though a tentative agreement had been negotiated to allow the cargo in after Red Cross inspections.
The trucks are reportedly heading to Luhansk, which is held by pro-Russian separatists. The Ukrainian military has been attempting to retake the stronghold with heavy shelling. According to reports, the fighting has led to shortages of water, food and power.
A rebel commander told The Associated Press that 34 trucks had gone through the border so far.
In a series of tweets on Friday, the International Red Cross said it was not escorting the trucks because of the "volatile security situation."
"We've not received sufficient security guarantees from the fighting parties," one tweet read. "Our team in Luhansk reports heavy shelling overnight."