An explosion ripped through an apartment building in the western Ukrainian city of Lviv on Thursday, injuring at least 10 people, emergency officials said. The blast, whose cause was not immediately known, occurred shortly after 4 p.m. in the city, located about 550 kilometers (340 miles) west of the capital, Kiev, the Emergency Situations Ministry said in a statement. Rescuers pulled 10 people from the rubble of the three-story building in the center of the city, including three young girls. One of the victims, an elderly woman, was in critical condition. Channel 5 television reported that officials believed that blast could have been caused by a natural gas leak or an explosive device planted in one of the apartments. An investigation was under way.