DONETSK, Ukraine — A barrage of rockets struck homes and a market in the Azov Sea port city of Mariupol in eastern Ukraine on Saturday, killing 27 people and wounding 97 others, the Interior Ministry said.

It was the latest indication that after a relative lull last fall, the war has flared up again in eastern Ukraine, with lethal artillery strikes landing in both rebel- and Ukrainian-controlled regions.

A leader of the Russian-backed rebels, Aleksandr Zakharchenko, has said his forces are now on the offensive, and on Saturday he said that an assault had begun against Mariupol, a strongly pro-Ukrainian seaside city with a prewar population of about 400,000 but now bulging with thousands of refugees from Crimea and elsewhere in eastern Ukraine.