Israeli aircraft fired missiles at the Palestinian prime minister's office early Sunday, just hours after a Palestinian official said the soldier whose abduction sent Israeli troops into Gaza is alive and in stable condition.

A Hamas militant was killed in another Israeli airstrike.

Palestinians witnesses said two missiles fired by attack helicopters hit the Gaza City office of Prime Minister Ismail Haniyeh of Hamas early Sunday, slightly injuring a bystander and setting the empty building on fire.

Inspecting his burning office, Haniyeh called the attack senseless.

"They have targeted a symbol for the Palestinian people," he said.

The Israeli military confirmed the attack and said it would "employ all means at its disposal ... to secure the safe return" of 19-year-old soldier Cpl. Gilad Shalit who was abducted by Palestinian militants on Sunday.

The strike, at about 1:45 a.m., came shortly after moderate Palestinian President Mahmoud Abbas warned Saturday that the coming hours would be "critical, sensitive and serious" for trying to calm the crisis.

In other airstrikes after midnight, Israeli aircraft hit a school in Gaza city and Hamas facilities in northern Gaza, where a Hamas militant was killed and another wounded, Palestinian officials said. The military said they were "planning terror attacks against Israel." The 34-year-old Hamas gunman was the second militant killed in the five-day Israeli operation to force the release of Shalit.

Ziad Abu Aen, a Palestinian deputy minister and Hamas official said Saturday that Shalit was wounded but in stable condition.

Another Hamas official, however, cast doubt on the credibility of the statement. Osama Muzami said only the military wing of the Islamic militant group knows the soldier's condition.

There had been no sign of Shalit since he was abducted during a militant raid on an Israeli army post just outside the Gaza Strip that killed two soldiers and two of the attackers.

Abu Aen said "mediators" told him Shalit had received medical treatment for wounds he suffered in the raid and was in stable condition.

"He has three wounds," Abu Aen said in the West Bank city of Ramallah. "I guess shrapnel wounds."

Israeli soldiers and Palestinian militants exchanged fire for several hours Saturday when Israeli tanks and bulldozers crossed into the Gaza Strip and began razing farmland east of Khan Younis. No serious injuries were reported.

The fighting took place north of the position Israeli troops occupied when they entered Gaza on Wednesday. The army said it was carrying out a limited operation in the Khan Younis area and the soldiers were expected to leave soon.

The Hamas-affiliated militants holding Shalit initially said they would trade information about him for all Palestinian women and underage prisoners in Israeli jails. The militants raised the stakes Saturday, calling for an end to the Israeli offensive and the release of 1,000 other prisoners in Israel, including some who are not Palestinian.

The new demand appeared aimed at rallying support in the Arab world.

Israel has ruled out any compromise, saying it would only encourage more abductions.

Israel continued to hold 64 Hamas leaders rounded up in the West Bank Thursday night. They include eight Cabinet ministers.

Israel has also blamed Syria for the kidnapping, noting it gives haven to Hamas' top leaders.

Defense Minister Amir Peretz met with senior security officials Saturday night and then called Secretary of State Condoleezza Rice to urge the Bush administration to step up pressure on Syria to work for Shalit's release, officials said on condition of anonymity because they were not authorized to make a statement.

Egypt and other foreign mediators have been working to try to resolve the crisis, but Abbas said those efforts had yet to bear fruit mainly because it was unclear who in Hamas, the militants or the group's leadership abroad, was authorized to make decisions about Shalit.

"The next hours are critical, sensitive and serious. And though the efforts are still ongoing, we have not reached an acceptable solution until now," Abbas' office said in a statement Saturday.

He sounded more optimistic at a news conference Saturday night.

"Regarding the soldier, we will surely reach an agreement. It is not a dead end. People want an acceptable solution," said Abbas, who is from the moderate Fatah Party.

Hamas, which controls the Palestinian Cabinet after winning legislative elections in January, insisted Shalit should not be freed without a prisoner swap.

Israel "should understand that it is not easy for the Palestinian people to say, 'OK, we can release him,' ... without a price," said Ghazi Hamad, a spokesman for the Hamas-led Cabinet.

Prime Minister Recep Tayyip Erdogan of Turkey, a predominantly Muslim country that has close ties with Israel, called President Bush Saturday and talked for 30 minutes about the crisis.

"The president said that the initial goal should be freeing the Israeli soldier, that is the key to ending the crisis," said Frederick Jones, spokesman for the National Security Council at the White House.

Meanwhile, the fuel supply in Gaza dwindled after Israel cut off the flow through a pipeline. Gas stations across the territory ran dry, and human rights groups worried that if fuel shipments were not restored in the coming days, Gaza could face a humanitarian crisis as generators used to pump water and power hospitals stopped working.

Authorities have been relying on generators since an Israeli airstrike Tuesday destroyed Gaza's only power plant, knocking out 43 percent of the territory's electricity supply, the United Nations said. The remaining electricity comes from Israel.

The Israeli army said Israel had increased the supply of electricity to Gaza to make up for the power shortage and would work to allow food and fuel in over the coming days.