Israel fired missiles and sent tanks on a foray into Gaza on Wednesday, killing four Palestinians in the deadliest military action since Hamas militants took control of the coastal strip.

At the same time, Israel allowed in a few sick and wounded Palestinians who had been holed up for days at a fetid border passage with Gaza.

A teenager with leukemia and four other Palestinians in need of medical care went through the tunnel at the Erez crossing in Israel, the military said. Israeli officials also authorized entry of all foreigners living in Gaza.

Mahmoud Abbas, the moderate Palestinian president, harshly criticized Hamas for its takeover of Gaza last week, referring to members of the group as "murderous terrorists." He accused Hamas of trying to assassinate him when he planned a visit to Gaza a month ago, digging a tunnel under a road where his car was to pass and trying to fill it with more than 550 pounds of explosives. Hamas denied the allegation.

Despite the turmoil, Abbas said peace talks with Israel should resume and appealed for international help in convening a peace conference.

A U.N. agency, meanwhile, warned of general food shortages in Gaza within weeks if the main cargo crossing with Israel wasn't reopened.

Israeli aircraft fired missiles at two rocket launchers in northern Gaza, in the first aerial attack on the strip since Hamas vanquished Abbas' rival Fatah. No injuries were reported in the strike, which came in retaliation for militant rocket fire on Israel.

Israeli tanks, meanwhile, rolled about 600 yards inside southern Gaza before dawn, and four militants were killed in a gunbattle, Palestinian hospital officials said.

Hamas and the allied Popular Resistance Committees said gunmen fired on undercover troops, prompting the army to send six tanks, two armored personnel carriers and a bulldozer to the area.

The army said the entrance of the troops had been planned, was not a broad operation, and was meant to counter militant activity, including arms smuggling.

In the West Bank, two Palestinian militants were killed in a predawn shootout with Israeli troops on an arrest raid on a house near Jenin, residents said. One was a local commander from the Islamic Jihad militant group and the other a local commander from a violent offshoot of Fatah.

The army said armed men opened fire from the house on troops, who shot back, killing two militants.

Mahmoud Zahar, the man widely believed to be leading Gaza's new Hamas rulers, said his group was open to a cease-fire with Israel if the army halts its activities there and in the West Bank. He said Hamas was capable of halting the frequent rocket attacks out of Gaza.

"But nobody will be the protector of the Israeli border," he told The Associated Press.

In an attempt to consolidate power, the West Bank-based government installed by Abbas on Sunday annulled all decisions made by the previous Hamas government, Information Minister Riyad al-Malki said.

All citizens will be required to change their travel documents to papers issued in the West Bank — in effect invalidating documents previously issued in Gaza, al-Malki said. And security personnel will be deployed in force in the West Bank to restore law and order, he added.

About 200 Gazans, petrified by the chaos in the Hamas-controlled coastal strip, have been camped out for six days in a tunnel reeking of trash, urine and sweat on the Palestinian side of the Erez crossing, pleading with Israeli authorities to grant them safe passage to the West Bank.

On Wednesday, Defense Minister Ehud Barak instructed officials to let in "humanitarian cases" at the crossing, the ministry said. No numbers were specified.

Saeb Erekat, a confidant of Abbas, said Israel had agreed to transfer 55 people to Israeli hospitals. Military spokesman Shlomo Dror would not confirm that number.

Military officials, who have said militants might try to squeeze through the passage, say not everyone in the tunnel is in danger. Israel, which has sophisticated weapons screening equipment in place at Erez, is only letting through the staff of international organizations and people with special permission.

Israel's Supreme Court began hearing a petition by a human rights group demanding that Israel also offer immediate medical treatment to 26 critically ill Palestinians hospitalized in Gaza.

Ran Yaron, a doctor with the group, said the lives of 15 of the patients represented in the petition — including a teenager with lupus and a child suffering from cancer — were in jeopardy because treatment was not available in Gaza.

The court said it would rule on the petition Monday.

Military liaison official Shadi Yassin said Hamas' takeover of Gaza deprived Israel of its main contact on humanitarian issues — Fatah-allied Palestinian police.

"Now, we don't have this contact, and are trying in every way to obtain information from the Red Cross about sick people whose transfer to Israel must be coordinated," he said.

The Red Cross coordinated the transfer Tuesday of seven Gazans wounded in internal strife, and hoped to arrange the transfer of six to nine more Wednesday, Red Cross spokesman Bernard Barrett said.

The U.N. World Food Program, meanwhile, began bringing in 225 tons of food into Gaza through Israel, in addition to 200 tons of food and medical supplies it sent in on Tuesday.

"There is a serious humanitarian crisis developing in Gaza as a result of the recent turmoil and closure of the border crossings," said Arnold Vercken, WFP director in the Palestinian territories.

Overall, more than 100 foreigners have left Gaza since Hamas wrested control, Dror said.

The U.N. Office for the Coordination of Human Affairs warned in a report that the reopening of Karni, the main cargo passage between Israel and Gaza, "is vital to prevent general food shortages in 2-4 weeks."

Israel also allowed in all foreign nationals in Gaza. Buses brought over some 90 Ukrainians, Yassin said, and Russia's ITAR-Tass news agency reported the evacuation of 69 Russian and seven Belarusian citizens was completed.

In a televised speech from the West Bank town of Ramallah, Abbas accused Hamas of attempting a coup.

"There is no dialogue with those murderous terrorists," Abbas said in his toughest remarks since installing his own Cabinet.

It's a fight between the national project and this small kingdom they want to establish in Gaza, the kingdom of Gaza, between those who are using assassination and killing to achieve their goals, and those who are using the rules of law," he said.

Abbas said he received videotapes of the operation to assassinate him, showing militants with Hamas signs on their shirts carrying out the work. He dismissed Hamas claims that the explosives tunnel was aimed at Israelis.

In Washington on Tuesday, President Bush and Israeli Prime Minister Ehud Olmert expressed support for Abbas at a high-profile news conference.

Olmert and Abbas will meet next week, Abbas aide Yasser Abed Rabbo told Palestinian radio. Olmert's office confirmed the two would meet but said a date had not been set.

On Wednesday, Israeli Foreign Minister Tzipi Livni telephoned Salam Fayyad, the prime minister of the new Cabinet Abbas installed after expelling Hamas from its governing coalition with Fatah, the Foreign Ministry said in a statement.

"The establishment (of the new government) facilitates progress on ... the peace process," the statement quoted Livni as saying.

Al-Malki characterized the conversation as "positive" and said, without elaborating, that it would be followed up by another phone call "to reach a quick and useful solution to all of the issues that need coordination with the Israeli side."

Hamas has found itself increasingly isolated diplomatically since the takeover, and has begun speaking publicly about dialogue with Fatah.

Ayman Taha, a Hamas spokesman in Gaza, said Cairo had invited the Islamic group for talks with Fatah, and that Hamas "welcomed" the invitation. There was no immediate response from Fatah, but an Abbas aide said Tuesday that dialogue with Hamas would be impossible until the group restored power to the legitimate government.