Inside the ghost town that's key to Ukraine conflict

The surrounding roads are littered with the wreckage of what were once Ukrainian military positions, an obliterated checkpoint, the remains of people in an armed personnel carrier hit by an explosion.

Inside the once bustling town, the icy, devastated, streets are empty. The few civilians too old or sick to flee cower indoors desperately, hoping not to be killed by the near-constant shelling.

Destruction doesn't discriminate, and nurseries have been hit by shells as well as City Hall, devastating the city's infrastructure.

This small transport hub in eastern Ukraine has become a focus for bitter violence between Ukrainian military and pro-Russian separatists following a ceasefire agreement four days ago that has faltered.

Most of Ukraine's armed forces have been pulled out of the strategic railroad town following weeks of fierce gunbattles and street fights, according to its military, while one rebel leader claimed that separatists had taken over 80% of the town.

Separatists claimed to have 60 Ukrainian prisoners of war, although CNN cannot independently verify those claims.

If you hadn't heard of Debaltseve before today, it's not surprising.

It was a small, nondescript Soviet-era town, which had a population of just 25,000 before fighting started.

So why exactly has it become a key focus for violence?

(CNN)