Russia sent a convoy of hundreds of trucks filled with aid into conflict-torn Ukraine on Friday without permission, prompting officials from the capital Kiev to accuse Russia of an "invasion," the Associated Press reported.

Ukrainian and Russian officials reached a deal to allow the convoy across the border into the eastern city of Luhansk as long as it was escorted by the Red Cross.  But Red Cross officials said they had not yet received enough security guarantees concerning how the aid is to be administered.

"The Russian side has decided to act," Russia's Foreign Ministry said on its website, accusing Ukraine of stalling the delivery of aid and killing civilians in the rebel strongholds of Luhansk and Donetsk.  

Ukraine, which feared the convoy was a ploy to help the rebel uprising, said the convoy crossing the border is a "direct invasion," the AP reported.   

 "This is a direct invasion done under the cover of the Red Cross for the first time ever," Valentyn Nalyvaichenko, Ukraine's security service chief, told the AP. "These are military men who have been trained to carry cargo, trained to drive combat vehicles, tanks and artillery."

Nalyvaichenko said the trucks would be used to transport weapons to the pro-Russian separatists and to recover the bodies of Russian fighters killed in Ukraine, the AP reported.

The Red Cross tweeted a statement saying it was not escorting the trucks due to safety concerns from repeated shelling in Luhansk overnight.

"We've not received sufficient security guarantees from the fighting parties."

The trucks were among hundreds that left a military base near Moscow last week but were stalled at the border with Ukraine over fears of what awaited inside the convoy. Russia says it's filled with 2,000 tons of aid, including food, water for civilians suffering in Luhansk, where intense shelling between rebels and Ukraine troops has been underway.

Russia in return has denied any attempt to help the separatists throughout the four-month conflict.

The trucks, which were reportedly re-painted white before leaving the military base, are suspected to not contain as much aid as Russia claims. AP journalists at the scene reported hearing objects sliding around inside the vehicles, suggesting that some were mostly empty.