The U.N. Security Council scheduled an open meeting Thursday in response to Palestinian calls for it to condemn Israel's killing of 18 members of an extended family and demand the withdrawal of Israeli troops from the Gaza Strip.

Palestinian U.N. observer Riyad Mansour said it was time for the U.N.'s most powerful body to shoulder its responsibilities with regard to the Israeli offensive in Gaza, a view backed by Arab and Islamic nations and the 117-member Nonaligned Movement of developing countries.

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The deaths in Gaza came early Wednesday, when Israeli artillery shells ripped through a residential neighborhood in the northern Gaza town of Beit Hanoun, killing at least 18 people, including eight children as they slept, according to Palestinian health officials and witnesses.

It was the highest number of Palestinian civilians killed in a single strike since fighting erupted six years ago, and undermined Palestinian President Mahmoud Abbas' attempts to form a more moderate government and renew a peace process with Israel.

"The Israeli occupying forces have committed another massacre this morning in Beit Hanoun," Mansour said. "The Security Council has to react and to react immediately in order to stop this aggression and these crimes against the Palestinian people."

The Palestinians want the council to adopt a resolution condemning recent Israeli attacks, particularly Wednesday's killings, and demanding an end to Israeli "aggression," a withdrawal of Israeli forces from Gaza, a mutual cease-fire and the deployment of U.N. observers on the Israeli-Gaza border, Mansour said.

Qatar, the only Arab nation on the Security Council, had asked for an emergency council meeting Monday on the Israeli offensive along the northern Gaza border. Israel says the offensive is aimed at halting Palestinian rocket fire on Israeli communities near the coastal strip.

U.S. Ambassador John Bolton said Qatar's request was discussed by the council on Tuesday "and there was no support for it."

The council revisited the request after Wednesday's attack, and France's U.N. Ambassador Jean-Marc de La Sabliere said members agreed on the open meeting Thursday.

The bloodshed in Beit Hanoun followed a weeklong Israeli takeover of the town in pursuit of militants who launch rockets at southern Israel. More than 50 Palestinians, most of them gunmen, were killed before Israeli troops withdrew on Tuesday.

The Israeli army said it had fired artillery at suspected rocket launching sites early Wednesday, but the targets were far away from the apartment compound. Israeli Prime Minister Ehud Olmert expressed regret for the loss of civilian life, but the government said its military operations in Gaza will continue.

"We do not accept any more 'sorry' and 'mistakes' from the Israeli government when they continue repeating these massacres in Gaza," Mansour said. "Those who are responsible should be brought to justice."

U.N. Secretary-General Kofi Annan expressed "anguish and deep concern about the loss of civilian lives." He said a full investigation has been initiated.

"In the meantime, I hope measures will be taken to ensure that the kind of incident we had this morning does not happen, and that both sides will be conscious of their obligations with regards to international humanitarian law and the protection of civilians," Annan said.

Israel launched its offensive in the Gaza Strip in June after Hamas-linked Palestinian militants captured an Israeli soldier, 19-year-old Corporal Gilad Shalit.

The United States blocked an Arab-backed U.N. resolution several weeks later that would have demanded Israel halt the offensive, the first U.N. Security Council veto in nearly two years.

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