Israel destroyed the homes of more than a dozen Hamas operatives and bombed one of its mosques on Friday, the seventh day of a blistering offensive in Gaza and the day after a deadly strike killed a prominent Hamas figure.

In what appeared to be a new Israeli tactic, the military called at least some of the houses ahead of time to warn inhabitants of an impending attack. In some cases, it also fired a sound bomb to warn away civilians before flattening the homes with powerful missiles, Palestinians and Israeli defense officials said.

Israel launched the aerial campaign last Saturday in a bid to halt weeks of intensifying Palestinian rocket fire from Gaza. The offensive has dealt a heavy blow to Hamas, but has failed to halt the rocket fire. New attacks Friday struck apartment buildings in a southern Israeli city. No serious injuries were reported.

After destroying Hamas' security compounds, Israel has turned its attention to the group's leadership.

In airstrike after airstrike early Friday, Israeli warplanes hit some 20 houses believed to belong to Hamas militants and members of other armed groups, Palestinians said.

They said the Israelis either warned nearby residents by phone or fired a warning missile to reduce civilian casualties. Israeli planes also dropped leaflets east of Gaza giving a confidential phone number and e-mail address for people to report locations of rocket squads. Residents stepped over the leaflets.

Israel used similar tactics during its 2006 war in Lebanon.

Most of the targeted homes Friday belonged to activist leaders and appeared to be empty at the time, but one man was killed in a strike that flattened a building in the Jebaliya refugee camp in northern Gaza.

More than 400 Gazans have been killed and some 1,700 have been wounded in the Israeli campaign, Gaza health officials said. The number of combatants and civilians killed is unclear, but Hamas has said around half of the dead are members of its security forces and the U.N. has said more than 60 are civilians, 34 of them children.

Three Israeli civilians and one soldier have also died in the rocket attacks, which have reached deeper into Israel than ever before, bringing an eighth of Israel's population of 7 million within rocket range.

The mosque destroyed Friday was known as a Hamas stronghold, and the army said it was used to store weapons. Hamas has boasted that more than 100 of the mosque's worshippers have been killed in the past on missions against Israelis.

It also was identified with Nizar Rayan, the Hamas militant leader killed Thursday when Israel dropped a one-ton bomb on his home. The explosion killed 20 people, including all four of Rayan's wives and 10 of his children.

The strike on Rayan's home obliterated the four-story apartment building and peeled off the walls of others around it, carving out a vast field of rubble.

Rayan, 49, ranked among Hamas' top five decision-makers. A professor of Islamic law, he was known for his close ties to the group's military wing and was respected in Gaza for donning combat fatigues and personally participating in clashes against Israeli forces. He sent one of his sons on an October 2001 suicide mission that killed two Israeli settlers in Gaza.

Israel's military said the homes of Hamas leaders are being used to store missiles and other weapons, and the hit on Rayan's house triggered secondary explosions from the stockpile there.

Israeli defense officials said the military had called Rayan's home and fired a warning missile before destroying the building. That was impossible to confirm. The officials spoke on condition of anonymity because they were not authorized to discuss military tactics.

Israel has targeted Hamas leaders many times in the past, but halted the practice during a six-month truce that expired last month.

Most of Hamas' leaders went into hiding at the start of Israel's offensive. Rayan, however, was known for openly defying Israel and in the past had led crowds to the homes of wanted Hamas figures _ as if daring Israel to strike and risk the lives of civilians.

The offensive has not halted rocket fire at Israel, and a barrage landed in the city of Ashkelon early Friday. Two rockets hit apartment buildings, lightly wounding one man, police said. Sirens warning Israelis to take cover when military radar picks up an incoming rocket have helped reduce casualties in recent days.

The military said aircraft destroyed the three rocket launchers used to fire at Ashkelon.

Israel has been building up artillery, armor and infantry on Gaza's border in an indication the punishing air assault could expand with a ground incursion. At the same time, international pressure is building for a cease-fire that would block more fighting.

Israel appears to be offering an opening for the intense diplomatic efforts, saying it would consider a halt to the fighting if international monitors were brought in to track compliance with any truce with Hamas.

Concerned about protests, Israeli police said they would step up security and restrict access to Friday prayers at Jerusalem's al-Aqsa Mosque. Devout Muslims attend large, communal prayers on Fridays.

Police spokesman Micky Rosenfeld said thousands of police would be deployed throughout the city, and that only Palestinian men over the age of 50, along with women of all ages, would be permitted to enter. He also said that police were in contact with Muslim leaders to ensure things remain quiet.

The army also imposed a closure on the West Bank, barring nearly all of the area's more than 2 million Palestinians from entering Israel.