Following reports Friday morning by the Ukrainian government that Russian military vehicles had entered Ukraine this week, the American and British governments warned Russia that using humanitarian assistance as a pretension for sending soldiers into rebel-held eastern Ukraine would be unacceptable to the West.

An intervention of the sort would be “deeply alarming” and “viewed as an invasion of Ukraine,” said Samantha Powers, U.S. ambassador to the United Nations, at a UN Security Council meeting regarding the deteriorating human rights situation in eastern Ukraine, the AP reported. Government forces are fighting pro-Russian separatists while military alliance North Atlantic Treaty Organization (NATO) estimates Moscow has sent about 20,000 troops to the border.

Powers cited Russia’s proposal to create “humanitarian corridors” to deliver aid to the rebels.

"The humanitarian situation needs addressing, but not by those who have caused it," she said. Instead, the Ukrainian government could create those corridors to help civilians escape the area.

"I am deeply concerned by reports of an increased flow of heavy weapons crossing into Ukrainian sovereign territory from Russia and by reports of Russian armed forces exercising for a 'humanitarian intervention' in a third country,” said Philip Hammond, the U.K. foreign secretary. "The conditions for such an intervention in eastern Ukraine manifestly do not exist. In these circumstances, such an intervention would be unjustified and illegal."