Russia threatens to escalate the situation in Eastern Ukraine by hinting at sending forces over the border. In response, Western nations have warned Russia against such actions, which would be considered an invasion.

During a meeting of the U.N. Security Council, U.S. ambassador to the U.N. Samantha Power warned Russia against sending troops into rebel-held Ukraine in the guise of humanitarian aid, according to The Associated Press. NATO reported that around 20,000 Russian troops have gathered at Ukraine's border.

"The humanitarian situation needs addressing but not by those who have caused it," Power said and explained how Russia proposed to create "humanitarian corridors" to deliver aid. She instead suggested Russia allow international organizations like the Red Cross to carry out the operation.

However, Russia does not seem to heed the U.S. and EU warnings. There have been reports that Russian tanks amassing at the border with Ukraine have "MC" for Mirotvorcheskiye Sily or "Humanitarian Force" written on their sides. Citing The Interpreter, the blog War is Boring explains how a YouTube video showed the tanks with the markings before disappearing from the site.

Britain has also expressed its apprehension and has echoed the United States' warnings against Russia, according to BBC News.

"I strongly urge Russia to avoid any provocative actions," U.K. Foreign Secretary Philip Hammond said. "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."

Hammond warned that any Russian incursion into Ukraine would be deemed "unjustified and illegal," reported BBC News.

Russia, however, has also taken punitive action of its own, arresting five Ukrainian officers it says have committed war crimes, according to CNN. The officers were part of a group of Ukrainian troops that retreated into Russia earlier this month.

"The officers are suspected of bombing civilians in Donetsk and shelling Russian territory," according to CNN.