Troops on the front line of Ukraine's battle with Russian-backed rebels wonder if it's about to get much worse

Eastern Ukraine — Amid mounting fear that Russia was on the brink of a full-scale invasion, CBS News senior foreign correspondent Holly Williams and her team were near the front lines on Tuesday of the conflict between Ukrainian forces and Russian-backed rebels that has simmered for almost eight years. They witnessed heavy artillery fire.

Suspected Russian military vehicles were spotted in the two breakaway regions of Ukraine that President Vladimir Putin recognized as independent on Monday — a move that has drawn fierce international condemnation and is expected to bring a round of new international sanctions against Moscow.

Ukraine has accused Putin of trying to revive the Soviet Union, and the country's president is asking for more international help urgently. But as Williams reported, the war in the breakaway regions of Ukraine's eastern Donbas area has been underway since 2014.