Palestinian security officials said the explosion was an Israeli assassination attempt with a helicopter firing two missiles, but Israeli military official sources denied army involvement. Rather, they described it as a "work accident" a term used when bombs in preparation explode prematurely.
People in the area did not speak of seeing any helicopters over the building, though several said they heard one in the area at the time.
"I was walking and I heard a big explosion and everyone heard it," said Mohammed Jabai, 34, "There was helicopter in the area, but I didn't see it didn't shoot any missiles."
Jibril Rajoub, the chief of West Bank security for the Palestinians, refused to comment on the cause of the explosion.
Palestinians in the area the center of the Palestinian-controlled part of Hebron were digging through debris, searching for anyone beneath. Bulldozers pushed rubble aside; police and ambulances were on the scene.
Palestinian security sources identified the dead man as Rajai Abu Rajab, an activist in the Tanzime, the military wing of the Fatah party.
Soon after the explosion, heavy gunfire broke out at a valley between the Palestinian village of Beit Jalla and the Israeli neighborhood of Gilo, which is on the outskirts of Jerusalem.
According to Jerusalem spokesman Shmuel Ben-Ruby, Palestinians fired from Beit Jalla toward Gilo and Israeli soldiers responded. There were no immediate reports of injuries or damage.
Hebron, where about 450 Jewish settlers live in a heavily guarded enclaves among 130,000 Palestinians, is often a site of violence. Gunfire exchanges between Palestinians and Israeli forces have been frequent during the 10-month Palestinian uprising.
Earlier, a 25-year-old Palestinian was seriously injured in a gunfire exchange in the city.
Learn more about the history of the Arab-Israeli conflict.
Also Friday, Secretary of State Colin Powell said it might be useful to have Americans and other monitors oversee a cease-fire between Israel and the Palestinians.
That cease-fire suffered several blows this week a Palestinian suicide bombing Monday that killed two, Israeli incursions into Palestinian territory and Thursday's killing of three Palestinians by a Jewish extremist group.
Powell said at a news conference that "no mechanism has yet been established, and no people have been called for from different countries or organizations."
His remarks appeared to temper a joint call Thursday by Powell and the foreign ministers of other major industrialized countries that Israel and the Palestinians should agree to "third-party" monitors as the best way to try to halt he breakdown in a U.S.-engineered truce.
Powell said any monitoring would require the approval of both sides. "That's the only way monitoring would work," he said.
The Israeli government, which has resisted Palestinian efforts to internationalize the conflict, has shown some openness to observers from the United States joining Israeli and Palestinian monitors.
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