Barely hours before a possible cease-fire is scheduled to come into effect in eastern Ukraine, fighting between government forces and pro-Moscow rebels raged on around the city of Mariupol near the Azov Sea, media reports said Friday.

Residents of Mariupol told BBC that explosions could be heard close to the city late on Thursday and early Friday, as rebels are reportedly heading west from the recently captured city of Novoazovsk. Pro-Russia separatists, allegedly backed by the Russian military, had invaded and seized control of the strategically located port town of Novoazovsk on Aug. 28 -- a move the Ukrainian government called a direct Russian invasion. Continuous clashes have been reported in the region ever since, leading to the deaths of several Ukrainian soldiers.

A Ukrainian military source told Reuters that the military is preparing for an imminent rebel attack on the city before a potential cease-fire, which is scheduled to come into effect from 7 a.m. EDT on Friday.

Ukrainian President Petro Poroshenko had, on Thursday, told reporters that the cease-fire would only be implemented if talks between Ukraine, Russia and pro-Moscow rebels, to be held in Minsk on Friday, are successful.

“Ukraine is paying the highest price,” Poroshenko reportedly said, “including lives of soldiers and innocent civilians. As president of Ukraine I must do my best to stop it.”

On Wednesday, Russian President Vladimir Putin had announced a seven-point plan, including a halt to "active offensive operations" by the Ukrainian military and pro-Russia rebels, international cease-fire monitoring, unconditional prisoner exchanges and humanitarian aid corridors. However, fighting in the Donetsk and Luhansk regions of eastern Ukraine has reportedly continued unabated after the announcement.

A British government official told BBC that if a truce fails to materialize, the European Union and the U.S. might announce tougher punitive measures against Russia, including more restrictions on Russia's banking, energy and defense sectors. However, further sanctions may be waived depending on the outcome of the negotiations in Minsk, the official added.