At least four Palestinians were killed on Thursday and over 30 injured when an unexploded ordnance (UXO), from last summer’s Israeli military offensive went off, while clearing rubble from a destroyed house in the southern Gaza Strip, medics said.

Palestinian medical sources at the Abu Yousif al-Najjar hospital in Rafah said four bodies and multiple wounded Palestinians arrived at the emergency room.

According to Ma’an, the victims, who were all from the same family, were identified as Hasan Abu Noqira, 45, Bakr Hasan Abu Noqira, 22, Abdul-Rahman Abu Noqira, 21, and Ahmad Hasan Abu Noqira, 38.

More than 30 Palestinians were injured, at least four of them suffered life-threatening wounds.

Over 7,000 unexploded ordnance were left throughout the Gaza Strip following last summer’s war between Israel and Palestinian militant groups, according to officials of the UN Humanitarian Coordinator for the Palestinian territories (OCHA).

Even before the most frequent Israeli assault, unexploded ordnance from the 2008-9 and 2012 offensives was a major threat to Gazans.

A 2012 report published by the Office of the High Commissioner for Human Rights said that 111 civilians, 64 of whom were children, were casualties to unexploded ordnance between 2009 and 2012, reaching an average of four every month in 2012.