Donetsk, Ukraine
Ukrainian servicemen ride atop an armored personnel carrier (APC) as they patrol an area near Donetsk on Aug. 11, 2014. Reuters/Valentyn Ogirenko

Update as of 7:07 a.m. EDT: Ukraine has said it will deny entry to 280 Russian trucks bound for eastern Ukraine with aid supplies, Associated Press reported.

"This convoy is not a certified convoy. It is not certified by the International Committee of the Red Cross," Andriy Lysenko, a spokesman for Ukraine's National Security and Defense Council, said according to AP.

Russia said Tuesday that 280 trucks have left for eastern Ukraine with at least 2,000 tons of humanitarian aid supplies, including food and medicine, following an agreement that was reached between Russia and Ukraine on Monday.

The trucks reportedly left from Naro-Fominsk, nearly 48 miles southwest of Moscow, carrying 12,000 sleeping bags, 400 metric tons of grain, 100 tons of sugar, 62 tons of baby food, 54 tons of medicine, and 69 portable power generators. However, NATO and the U.S., who have said that Russia has not yet moved its forces away from the Ukrainian border, are reportedly concerned that the move might be a screen for a potential military invasion on Ukraine.

"We see the Russians developing the narrative and the pretext for such an operation under the guise of a humanitarian operation, and we see a military build-up that could be used to conduct such illegal military operations in Ukraine," NATO Secretary-General Anders Fogh Rasmussen, said Monday.

The trucks are reportedly painted white with a red cross on it and, according to Al Jazeera, the convoy is reportedly moving toward Luhansk, without any armed escorts. More than 1,300 people have been killed since April, and 850,000 people have been forced to flee their homes in eastern Ukraine, since pro-Russian separatists began clashing with the Ukrainian military in February.

Andre Loersch, a spokesperson for the International Committee of the Red Cross mission in Ukraine, said, according to Associated Press, that he had no information about the content of the convoy and where the trucks were headed, but added: “At this stage we have no agreement on this, and it looks like the initiative of the Russian Federation.”

Marie Harf, deputy spokesperson at the U.S. Department of State said, at a briefing on Monday: “We believe Russia’s been trying to lay the international groundwork to support a humanitarian operation into Ukraine. We are concerned that Russia could try to use a humanitarian or peacekeeping operation as a pretense for inserting elements of military force into Ukraine. We do not believe that any actions, humanitarian or otherwise, should be taken in Ukraine without Kyiv’s direct permission.”