The deadly attack came a few hours after Palestinians in Gaza fired rockets at Israeli towns, and Israeli forces wound up a phase of a wide-ranging operation in a Palestinian refugee camp on the Egyptian border.
Security sources, speaking on condition of anonymity, said Palestinians ambushed an Israeli army foot patrol in the Palestinian village of Ein Yabrud, east of the West Bank town of Ramallah. Three soldiers were killed and another was seriously wounded, they said.
The area has been the scene of frequent Palestinian gunfire attacks against Israeli military and civilian vehicles. There was no immediate claim of responsibility.
Israel TV said that because of the severity of the attack, Israeli forces were likely to enter Ramallah, where Palestinian leader Yasser Arafat has been trapped in his headquarters for nearly two years.
Israel Radio reported that soldiers imposed a curfew on Ein Yabrud and was searching for the attackers, who escaped.
The last serious attack if its kind in the area was in February last year, when four Palestinian gunmen opened fire an Israeli military checkpoint at nearby Ein Arik, killing six soldiers before escaping.
Earlier Sunday in Gaza, Palestinian militants fired a barrage of homemade rockets from Gaza into Israel, one of the largest salvos in months.
No one was hurt in the barrage of Qassam rockets, relatively small and primitive weapons. Three exploded in the town of Sderot, a frequent target less than one mile from the Gaza border fence, and others fell near smaller communities, the military said.
Palestinian militants make the rockets in Gaza workshops. They have a range of about five miles. Although no one has been killed in the attacks, Sderot residents and officials have called on the government to take action to stop the salvos.
In the past, similar rocket attacks have prompted Israeli military reprisals. An army spokesman declined to discuss plans for an Israeli response but said the military is always prepared to defend its citizens.
The military said last week, militants fired nine Qassam rockets, but only three landed in Israel, causing no damage or casualties.
Also Sunday, Israeli forces wound up another phase of a large-scale operation in another part of Gaza — near the Egyptian border.
After pulling out of the Brazil section of the sprawling Rafah refugee camp following a four-day sweep, troops continued to operate in other parts of the border area. The troops and tanks redeployed along the Egyptian border, just a few hundred yards from the camp, witnesses said.
Israel launched its broadest military operation in six months in the Rafah area of Gaza on Oct. 10, six days after an Islamic Jihad suicide bombing in a Haifa restaurant killed 21 people.
Soldiers moved into the Brazil camp last Thursday, the third part of the camp to be targeted. Troops demolished at least 15 homes in the Brazil neighborhood, killing four gunmen and four bystanders, witnesses said.
Troops left behind roads destroyed by tanks and wrecked water pipes, residents said. Electric and telephone cables were also torn apart, they added.
Israel claims Palestinians use tunnels — sometimes hidden under homes — to smuggle arms from Egypt into the Gaza Strip. The military has said it has intelligence warnings that the Palestinians might be trying to smuggle more advanced weapons, such as anti-aircraft missiles.
During the entire Rafah operation, 14 Palestinians — including two children and a woman — were killed.
About 114 homes were destroyed at the start of the Rafah military operation, leaving about 1,240 Palestinians homeless, according to the U.N. Relief and Works Agency, which aids Palestinian refugees.
Israeli Defense Minister Shaul Mofaz told the Cabinet on Sunday that troops had so far uncovered four tunnels in the Rafah area and that the raids would continue until other tunnels are uncovered, a senior government official who attended the meeting said.
In the West Bank town of Jenin, meanwhile, troops backed by tanks and armored jeeps raided offices of the militant group Islamic Jihad, confiscating computers and documents, witnesses said. Two militants were arrested, witnesses and the army said. The army said the militants were planning suicide attacks in Israel.
Also Sunday, Israel's army used emergency orders to call up five reserve battalions — about 1,800 soldiers — to replace soldiers serving in the West Bank and Gaza Strip. Such short-notice call-ups are unusual. Israel Radio said the reason was an increase in intelligence warnings of terror attacks.