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JERUSALEM (CNN) -- Israeli Prime Minister Ehud Olmert on Thursday blamed a "technical error" for the military's tank shelling of Beit Hanoun that killed 19 Palestinian civilians, mostly women and children, according to a spokeswoman with the minister's office.

The bloodshed happened early Wednesday, hours after Israel announced it had pulled out of the northern Gaza town where it was targeting militants firing Qassam rockets into Israel.

Israeli tanks, poised on the outskirts of Beit Hanoun, fired 10 artillery rounds into the town's center and killed 19 people, Palestinian medical sources said. (Watch villager describe how relatives were 'cut to pieces' -- 2:40)

Among the dead was a 13-member family that included seven children, the sources said.

Israelis, Palestinians alike outraged

The deaths have been labeled a massacre by moderate and hard-line Palestinian leaders, and have prompted outrage among Israelis, Palestinians and the international community.

The Associated Press reported that 18 were killed, members of an extended family. (Full story)

Hours after the incident, which is under investigation, Olmert and Israeli Defense Minister Amir Peretz expressed their regret over the civilian deaths.

Israel Defense Forces said units "fired preventative artillery" at rocket launch sites in Beit Hanoun to "disrupt and thwart the launching of Qassam rockets."

In a statement, U.N. Secretary-General Kofi Annan expressed shock at the attack, and renewed a call to the Israeli government to stop its military operations in Gaza, without delay, and the Palestinians to halt attacks against Israelis.