GAZA CITY, Gaza Strip - A mysterious blast after nightfall Monday leveled a building in Gaza City, killing four people and wounding at least 30, residents and hospital officials said. The violent Islamic Hamas group blamed Israel, but the Israeli military said it was not involved.

The explosion came hours after Palestinian security forces got their first look at demolished Jewish settlements in Gaza, touring the area ahead of Israel's formal handover in mid-September. The joint tour by Palestinian commanders and Israeli military officials marked the first time Palestinian authorities were allowed into the settlements, which were evacuated two weeks ago.

The blast in the Gaza City neighborhood of Shajaiyeh destroyed a house where known Hamas members lived. Hamas charged that an Israeli missile hit the house, with a group spokesman, Munir al-Masri, accusing Israel of continuing its "dirty assassination policy, which gives us the right to respond and to defend ourselves."

Some residents said it was apparently a case of explosives in the house detonating prematurely as Hamas militants worked on a bomb.

Palestinian leader Mahmoud Abbas called the explosion "regrettable" and said "security is investigating the cause."

Israeli aircraft have often raided the neighborhood, targeting Palestinian militants, but the raids all but stopped after a cease-fire went into effect in February.

Also Monday, an Israeli official said Egyptian President Hosni Mubarak was planning to visit in November, another diplomatic dividend from Israel's Gaza pullout. However, Mubarak's spokesman said he had no such plans.

Israel is trying to revive low-level ties with Muslim nations that languished during more than four years of Israel-Palestinian conflict - as well as trying to establish new ones. Palestinians are unhappy with Israel's recent successes, however, and have urged Muslim nations to freeze ties with Israel until a final peace deal is reached.

Mubarak will travel to Israel in November to attend a service marking 10 years since the assassination of Prime Minister Yitzhak Rabin, the official said, speaking on condition of anonymity because he wasn't authorized to make a formal announcement.

However, Mubarak's spokesman Suleiman Awad told The Associated Press, "I can assure you that the president doesn't have any plans to go anywhere outside Egypt until the end of this year."

"He is quite busy with so many things, the presidential and legislative elections, and doesn't have any plans to go anywhere outside Egypt," the spokesman added.

The Egyptian leader has not visited Israel since Rabin's funeral in 1995, and Israeli officials interpreted his planned visit as sending a message to other Arab and Muslim countries that Israel should be rewarded for evacuating 21 settlements in Gaza and four in the West Bank.

Jordan's King Abdullah is also planning to visit Israel, Israeli government officials have said, but Jordanian officials have not confirmed that.

Saeb Erekat, a Palestinian negotiator, said Israel must first make peace with the Palestinians if it wants full relations with the Arab and Muslim world.

"Once we make peace, once the occupation is over, once there is a Palestinian state, (Israel) will have full normal relations," Erekat said.

Israel made progress last week when Foreign Minister Silvan Shalom met publicly for the first time with his Pakistani counterpart, Khursheed Kasuri. However, Palestinian President Gen. Pervez Musharraf said there would be no full relations with Israel until a Palestinian state is established.

A five-member Israeli delegation is currently in Tunisia planning Shalom's November visit to participate in a U.N. conference, Regev said.

The trip to Tunisia has special significance for Shalom, who was born there in 1958. He immigrated to Israel when he was one year old and has never been back.

Also Monday, dozens of unemployed workers in the Palestinian town of Khan Younis demonstrated outside a municipal building, demanding jobs and better living conditions.

For a second straight day, the protest escalated into violent clashes with security forces. Protesters pelted riot police with stones and firebombs, and police fired into the air in an attempt to control the crowd.

The Palestinian Interior Ministry said seven officers and three civilians were wounded.