(Reuters) – Ukrainian government forces came under artillery fire late on Saturday near the strategic port of Mariupol in eastern Ukraine, in the first serious violation of a ceasefire declared only about 30 hours earlier.

The presidents of Russia and Ukraine had earlier said the ceasefire, part of a peace road-map intended to end five months of conflict, was largely holding across eastern Ukraine, where Kiev’s forces have been battling pro-Russian separatists.

A Reuters reporter heard prolonged artillery fire late on Saturday to the east of Mariupol, a key flashpoint in the past week of fighting, and then saw a truck, a gas station and an industrial facility ablaze within the limits of the city.

The reporter also saw trucks rushing eastwards conveying agitated-looking pro-government militia volunteers. Tanks and armored personnel carriers also headed in the same direction.

“There has been an artillery attack. We received a number of impacts. We have no information about casualties,” a Ukrainian officer told Reuters.