Russia is reportedly sending troops and heavy weapons into areas of Ukraine controlled by pro-Russia rebels, intensifying the conflict and stoking fears that Russia could invade further into Europe.
On Sunday, the Ukrainian military reported "intensive" movement of troops and equipment, with reports of 20 trucks headed to the rebel-held city of Donetsk. AFP reporters saw anti-aircraft guns headed toward the government-held airport.
"There is intensive deployment of military equipment and personnel of the enemy from the territory of the Russian Federation onto territory temporarily controlled by insurgents," Ukrainian military spokesman Andriy Lysenko told a briefing in Kiev.
There has been a cease-fire between Ukrainian rebels and the government for nearly two months, but it has been violated daily in the zone along the Russian border. Russian troops have also occupied Ukraine's southern province of Crimea, which it has declared part of Russia.
The latest invasion comes amid fears that Russia and President Vladimir Putin may have aspirations to invade other parts of Europe. Within the past week, Russia sent more than a dozen aircraft to test NATO defenses across northern Europe. Russia also test-launched a ballistic missile in the Barents Sea, north of Sweden.
U.S. officials believe the acts could be a dry run of sorts to prepare for military strikes.
"That could certainly be the case," retired Air Force Lt. Gen. David Deptula, the service's influential former intelligence chief, told the Daily Beast. "It is not farfetched that at some point within the next two years [Russian President Vladimir] Putin makes a more aggressive move in Eastern Europe and uses a nuclear threat to deter a NATO response."
Vladimir Putin has also made other aggressive moves, including reports that he bragged of Russia's ability to invade Europe if they so wished. The German newspaper Sueddeutsche Zeitung reported that Putin bragged to Ukrainian President Petro Poroshenko and European Commission President Jose Manuel Barroso that Russia could invade beyond Ukraine.
"If I wanted, in two days I could have Russian troops not only in Kiev, but also in Riga, Vilnius, Tallinn, Warsaw and Bucharest," Putin reportedly said.
The Russian troop buildup took place amidst elections in Ukraine, which Russia said it would recognize.