Three Palestinians -- one each from Hamas, Islamic Jihad and the Al Aqsa Martyrs' Brigade -- slipped into an Israeli army (search) post Sunday and killed four soldiers before being killed by troops.
The shooting, a possible setback to a U.S.-backed "road map" for Mideast peace, came just hours after radical Palestinian groups said attacks on Israelis would not be interrupted. After the killings, Israel quickly demanded Palestinian officials crack down on extremists.
Hamas, Islamic Jihad and the Al Aqsa Martyrs' Brigade claimed joint responsibility for the attack. A leaflet gave the names of the gunmen, all in their early 20s, one from each group.
"This joint operation was committed to confirm our people's united choice of holy war and resistance until the end of occupation over our land and holy places," the leaflet said.
The attack is a blow to efforts by Palestinian Prime Minister Mahmoud Abbas (search) to persuade militants to halt attacks on Israelis -- his strategy for bringing a halt to violence as required under the U.S.-backed plan.
Hamas pulled out of truce negotiations last week, and the Al Aqsa militia's participation in the shooting poses a direct challenge to Abbas, since the group is linked to his ruling Fatah (search) movement.
The gunmen, who wore Israeli army uniforms and were armed with assault rifles and grenades, attacked the post near Gaza's Erez crossing into Israel just after dawn, the Israeli military said.
Maj. Gen. Doron Almog, head of the army's southern command, told Israel Radio the attackers arrived by surprise at the northern edge of the post, and killed the four soldiers, three of them at close range. Four other soldiers were wounded.
In Hebron, Palestinians opened fire on Israeli troops in two separate attacks near a disputed holy site. The first attack wounded an Israeli policeman; in the second, an Israeli was killed before soldiers shot and killed two Palestinian attackers, the military said.
Israel demanded Abbas immediately begin arresting extremists, dismantling their organizations and disarming Palestinians.
"If terrorism will continue, it will destroy the road map, it will destroy the peace process," Israeli government spokesman Avi Pazner said.
Abbas said he would resist pressure to crack down on the militants and would continue efforts to talk with them.
"We will not allow anybody to drag us into a civil war," Abbas said Sunday.
Palestinian Foreign Minister Nabil Shaath said Israel provoked the attacks by continuing restrictions on Palestinians and killing two Hamas militants Thursday night near the West Bank city of Tulkarem.
"This requires an immediate discussion with the Palestinian factions to bring an end to the fighting and there is an effort from all sides to make sure that this happens," Shaath said.
The shooting underscored the determination of militants to derail the road map to Mideast peace, which envisions a Palestinian state by 2005.
Abdel Aziz Rantisi, a Hamas leader, said the attack was intended to send a message to the Palestinian leadership that Palestinians will continue to fight Israel and will not "surrender to the pressure exerted by Israel and the United States of America."
"We are unified in the trenches of resistance," he said.
A videotape sent to The Associated Press shows the three attackers wearing army uniforms and sitting in front of the three flags of their militant groups. Three copies of the Quran, two rifles and several hand grenades lay on a table in front of them.
The attack came hours after an armed Palestinian tried to attack a Jewish settlement in Gaza, according to Palestinian and military sources.
Israeli troops killed the man, who was armed with an assault rifle and a pouch of grenades, after he fired at them Saturday night from a house in the central Gaza Strip, military sources said.
In a statement faxed to the AP, the radical Democratic Front for the Liberation of Palestine claimed responsibility for the attack and said the man had been trying to infiltrate a nearby Jewish settlement.
The three-stage peace plan was formally launched at last week's Mideast summit in Jordan, with President Bush, Israeli Prime Minister Ariel Sharon and Abbas attending.
Sharon was set to defend his support of the plan at a meeting of his hawkish Likud party Sunday night.
Success of the road map depends to a large extent Abbas' ability to rein in the militant groups. Abbas has said he will not use force against the armed groups for fear of civil war, and as recently as last week appeared confident he could negotiate a truce with them.
However, Hamas, the most deadly of the groups, walked away from truce talks Friday, saying Abbas made too many concessions at the summit, where he condemned violence against Israelis and called for an end to the "armed intefadeh."
On Saturday, Hamas met with Islamic Jihad and other radical factions, and participants agreed they would not stop bombings and shootings. "All agree on our peoples rights to resist occupation," Rantisi said after the meeting.
Reflecting the continuing tension, Israel reimposed a closure on the West Bank, banning Palestinians from entering Israel, except for humanitarian cases. The military said the closure was in force as of midnight, "due to serious security alerts."
After Sunday's shooting, Gaza crossings into Israel were also closed. Israeli security sources said there have been dozens of warnings of planned terror attacks.
Sharon had eased a previous closure a week ago as a goodwill gesture to Abbas ahead of the summit.
Palestinian officials had said before Sunday's attack that the Hamas walkout may not be final and there's still a chance for a truce.
The Associated Press contributed to this report.