Update — 12:55 p.m. ET
Russian artillery units, manned by members of the military fired on Ukrainian armed forces, NATO officials said on Friday
Oana Lungescu, a spokeswoman for NATO, told The New York Times that "Russian artillery support — both cross-border and from within Ukraine — is being employed against the Ukrainian armed forces."
The report comes as trucks in a Russian convoy, delivering aid to eastern Ukraine, crossed the border into the region on Friday without the permission of the Ukrainian government.
The trucks in the 200-vehicle convoy are said to be loaded with water, generators, and sleeping bags. The convoy's passage had been delayed for more than a week amid suspicions it was being used as cover for a Russian invasion.
Ukraine's Security Service Chief Valentyn Nalyvaichenko said the "invasion ... happened for the first time under the cover of the Red Cross," but added that Kiev would not use force against it.
The convoy also proceeded without support from the Red Cross, which has been accompanying its journey so far.
Nalyvaichenko has claimed the men driving the trucks are members of Russian military forces and trained to drive combat vehicles, and that the vehicles would go on to be used to transport weapons to the pro-Russian rebels and remove the bodies of fighters from eastern Ukraine, the Associated Press reported.
NATO's secretary general, Anders Fogh Rasmussen, criticized Russia's actions.
"I condemn the entry of a Russian so-called humanitarian convoy into Ukrainian territory without the consent of the Ukrainian authorities and without any involvement of the International Committee of the Red Cross," he said.
"These developments are even more worrying as they coincide with a major escalation in Russian military involvement in Eastern Ukraine since mid-August, including the use of Russian forces," he said.
According to Interfax, 34 KamAZ trucks have crossed through the Izvaryne checkpoint.
The trucks are bound for the city of Lugansk, where pro-Russian separatists are besieged by Ukrainian government forces. They contain generators, blankets, water, and sleeping bags intended for civilians. The city has been hit by shelling for several weeks.
There had been confusion over the Red Cross' role in the convoy's movements.
The organization had been pushing for a cease-fire to ensure the safe passage of their drivers through eastern Ukraine. However, since no such truce came, there have been contradicting claims as to whether Red Cross drivers had been involved in crossing the border.
However, the International Committee of the Red Cross has tweeted that it is not escorting the trucks because of the nature of the security situation in the region.
A statement on the Russian foreign ministry's website reads: "The Russian side has decided to act. ... Our column with humanitarian aid is starting to move in the direction of Lugansk."