At least 21 people died in a large fire in the Gaza Strip. Among the victims are seven children, there are also wounded, Reuters reported. Witnesses claim that the entire residential building in the Jabalia refugee camp in the northern part of the Gaza Strip has burned down. Jabaliya is one of eight refugee camps in the region. The Gaza Strip is home to 2.3 million people, making it one of the most densely populated areas in the world, according to Reuters. The cause of the accident is currently unknown, but according to the local civil defense, a large amount of fuel was stored in the building, BTA adds. Palestinian leader Mahmoud Abbas described what happened as a national tragedy and declared today a day of mourning. Israeli Defense Minister Benny Gantz promised the authorities to assist in evacuating the wounded to Israeli hospitals.