Reporting from Tel Aviv and Jerusalem — The military power of Hamas has been weakened and its political leadership is divided over plans for a possible ceasefire, but an Israeli intelligence official said today that the radical group remains formidable, with 15,000 fighters and a sophisticated arsenal of rockets and anti-tank weapons and tunnels.

The senior official's assessment was delivered in a news briefing on a day when Israeli ground forces and Hamas fighters battled fiercely in a southeastern neighborhood of high-rise apartments in Gaza City. Civilians fled for cover as Israeli units, backed by shelling from warships along the seaside enclave, pushed deeper into the city but appeared to stop short of advancing toward Hamas strongholds.

Israel's move into the Tel Hawwa neighborhood of Gaza City -- about one mile from the city's center -- increases the pressure on Hamas fighters and on humanitarian groups and hospitals trying to cope with rising numbers of homeless and wounded Palestinians. Since Israel's incursion began Dec. 27, more than 900 Gazans, at least one-third of them women and children, have been killed.

Human Rights Watch and other international organizations have called for Israel to allow Palestinians to escape the fighting and for humanitarian groups to enter with medical supplies, food, fuel and equipment. Israel said it has allowed 22,000 tons of humanitarian aid and 1.3 million liters of fuel into Gaza, but much of the enclave has no electrical power, and pleas for donations echo endlessly from the loudspeakers of mosques.

"We don't know the full extent of what's happening inside Gaza because we are blocked from getting in," said Fred Abrahams, senior emergencies researcher for Human Rights Watch. "But what we are observing is a deeply disturbing disregard for human life."

The Israeli intelligence official, who spoke on the condition of anonymity, did not underestimate Hamas but indicated the group had been overwhelmed by 18 days of Israeli bombardment. The Israeli Defense Forces reported that at least 30 militants had been killed in fighting today and that Hamas was occasionally using suicide bombers as spearheads for its combat missions.

"The level of damage to Hamas' military wing is less than the damage" to its civil infrastructure, the official said. "I think they will try to do their best to hit us, to come up with some symbolic achievement, a suicide operation or the kidnapping of an Israeli soldier. This is something they very much want to succeed."

Israeli political leaders, including Foreign Minister Tzipi Livni, suggested that Israel was still hoping for an agreement on an Egyptian-backed ceasefire plan. Israeli security officials were expected to return to Cairo for talks on Wednesday. A Hamas delegation met with the Egyptians today, but there was no announcement of any breakthrough.