(Reuters) – Russia unleashed rockets on Tuesday on an encircled steel works in Mariupol, Ukraine’s last redoubt in the port city, after a ceasefire broke down with some civilians still trapped beneath the sprawling site despite a U.N.-brokered evacuation. FIGHTING * At least 10 people were killed and 15 wounded by Russian shelling of a coking plant in the city of Avdiivka in the Donetsk region of eastern Ukraine on Tuesday, the regional governor said. The Ukrainian president’s office said earlier other areas of Donetsk were under constant fire. * Russia has struck a military airfield near Ukra…