At least 22 Palestinians were killed in separate Israeli airstrikes and tank shelling Tuesday, a Palestinian health official said.

The death toll since the beginning of the Israeli Operation Cast Lead on December 27 rose to 573 with some 2,600 other wounded, said Mo'aweya Hassanein, chief of emergency and ambulance services in Palestinian Health Ministry.

Local witnesses said that after midnight Israeli warplanes fired eight missiles and bombed the largest security center, which was once the biggest security headquarter of Palestinian National Authority in Gaza. Several buildings, including prisons, military court and garages, were destroyed in the attack.

Gaza citizens said that Israeli tanks, warplanes and gunboats destroyed six houses across the Hamas-ruled Gaza Strip. This is why the death toll is so high since midnight and most of them are civilians, said the witnesses.

Israeli warplanes also bombed a school run by the United Nations in the beach refugee camp, killing three people, according to a UN statement.

Palestinian refugees in the school had to evacuate to other place after the strike, the statement added.

Meanwhile, al-Qassam Brigades, Hamas armed wing said in short messages sent to journalists that they claimed responsibility for the deaths of three Israeli soldiers last night. But according to Israeli Defense Force, the three soldiers were killed by a friendly fire incident.

The Israeli troops continued on Tuesday the military operations in Gaza for the 11th consecutive day.

(Xinhua News Agency January 6, 2009)