GAZA CITY, Gaza Strip — Israeli warplanes pounded the homes of Hamas leaders and ground troops edged closer to the Gaza Strip's densely populated urban center Monday, as Israel weighed a decision to escalate its devastating offensive.

Despite the tightening Israeli cordon, militants managed to fire off at least four rockets Monday morning. There were no reports of injuries, though one rocket hit a house in the southern city of Ashkelon.

Black smoke rose over Gaza City's suburbs, where the two sides skirmished throughout the night. At least six Palestinians died in the new airstrikes or of wounds on Monday, Gaza health officials said. One of the dead was a militant killed in a northern Gaza battle.

The army announced Sunday that it was sending reserve units into Gaza to assist thousands of ground forces already in the territory. The use of reserves is a strong signal that Israel is planning to move the offensive, which Gaza officials say has killed some 870 Palestinians, into a new, more punishing phase.

Israel launched the offensive on Dec. 27, bombarding Gaza with dozens of airstrikes before sending in ground forces a week later. The operation is meant to halt years of Palestinian rocket attacks on southern Israel. Fighting has persisted despite international calls for a cease-fire. Thirteen Israelis, including 10 soldiers, have died.

Egypt, which often serves as a mediator between Israel and Hamas, has been playing a key role in trying to forge a cease-fire. In Cairo, Egypt's state-owned news agency reported progress in truce talks with Hamas but provided no specifics.

International Mideast envoy Tony Blair was in Cairo on Monday, meeting with President Hosni Mubarak following talks with Israeli leaders on Sunday. Egypt has put forward a three-stage proposal to end the fighting.

"I think the elements of an agreement for the immediate cease-fire are there," Blair said, adding that, while more work needed to be done, he hoped to see a cease-fire "in the coming days."

Israel's representative to the talks, Defense Ministry official Amos Gilad, was in close contact with Egypt. But in a sign that more work is needed, he postponed a trip to Cairo, officials said.

With Israeli troops surrounding Gaza's main population centers, Israeli leaders have given mixed signals on how much further the army is ready to push, saying the operation is close to achieving its goals but vowing to press forward with overwhelming force.