Some 20 people were killed Saturday night when an Israeli airstrike targeted the home of the Hamas police chief in the Gaza Strip.

Palestinian sources put the number of dead at 21 on Sunday morning, although medics had earlier said that between 15 and 18 people were killed.

The police chief, Tayseer al-Batsh, was moderately injured. He underwent surgery and was reportedly in stable condition on Sunday morning. Most of the dead were members of his family.

The strike against al-Batsh’s house came as a large group of Palestinians exited an adjacent mosque after prayers. Many of them were injured, according to Palestinian reports.

In all, some 35 people were wounded in the strike.

Meanwhile, one more person was killed in southern Gaza’s Rafah in another strike that also injured five people, emergency services spokesman Ashraf al-Qudra said.

The strikes came after Hamas launched a barrage of long-range rockets at Israeli cities including Tel Aviv, after issuing a warning that it would strike.

Following the airstrike, Israel advised residents to leave parts of northern Gaza for their own safety.

The new deaths brought the toll in the fifth day of the conflict to 151, with more than 1,000 people wounded.

On Friday, the United Nations’ Office for the Coordination of Humanitarian Affairs said a majority of those killed in Gaza so far — 77 percent — were civilians.

The IDF said Sunday morning that since the outset of Operation Protective Edge in Gaza, it had struck “1,320 terror targets across the Gaza Strip, including 735 concealed rocket launchers, 64 training bases and militant compounds, 58 weapons storage and manufacturing facilities, 32 Hamas leadership facilities, 29 communications infrastructures and additional sites used for terrorist activities.”

AFP contributed to this report.