Story highlights Ukrainian army in Mariupol fears last-minute assault by separatists ahead of ceasefire

Army and rebels traded shots in several cities and towns in southeast Ukraine on Saturday

Talakovka, Ukraine (CNN) Artillery and rocket fire can be heard almost constantly in the village Talakovka, about 10 kilometers from the strategic port city of Mariupol in southern Ukraine.

The Ukrainian army has dug in here, fearing a possible last-minute assault by pro-Russian separatists ahead of a planned ceasefire late Saturday. Armored vehicles with cannons mounted on top fired from a front line position with tanks standing nearby.

The unit commander, who only identified himself as "Pavel," said he did not believe the ceasefire would hold.

"We know about this so-called ceasefire. We have had agreements before. The separatists have broken them frequently. But we will stick to the agreements and stop the violence coming from their side," he said as artillery barrages could be heard firing off in the distance.

Over his walkie-talkie a voice could be heard saying: "Our artillery is in action."

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