Four Israelis have been shot dead in the West Bank, Israeli police say.
Their vehicle came under fire on a road between the settlement of Kiryat Arba and the Palestinian village of Bani Naim, near the city of Hebron.
The military wing of the Palestinian Islamist movement, Hamas, said it had carried out the "heroic operation".
Prime Minister Benjamin Netanyahu said it showed there should be "no compromise" on Israeli security demands at the relaunched direct peace talks.
"The prime minister ordered the security forces to act without diplomatic limitations in order to catch the murderers," his spokesman, Nir Hefetz, said on arrival in the US ahead of Thursday's meeting between Mr Netanyahu, Palestinian Authority President Mahmoud Abbas and US Secretary of State Hillary Clinton in Washington.
"Terror will not determine Israel's borders or the future of the settlements," Mr Hefetz added.
Palestinian Authority Prime Minister Salam Fayyad also condemned the attack, saying it went "against Palestinian interests".
The White House condemned the killings in the "strongest possible terms," adding that all parties must "continue working to achieve a just and lasting peace in the region".
US state department spokesman PJ Crowley said: "There may well be actors in the region who are deliberately making these kinds of attacks in order to try to sabotage the process."
'Grave incident'The attack took place near Bani Naim after dark on Highway 60, a busy route used by both Palestinians and Jewish settlers.
The four victims - two men and two women, one of whom was pregnant - were reportedly shot at from a passing vehicle.
Video footage showed a white estate car standing at an angle
on the side of the road, its windows shot out and its doors riddled with
bullet holes. Officials said all four victims were from the Beit Haggai
settlement.
"Hamas praises the attack and regards it as a natural response to the crimes of the occupation”
End Quote Sami Abu-Zuhri Hamas spokesman"This was a terrorist attack and the army is treating it as a grave incident," Israeli army spokeswoman Lt-Col Avital Leibovich told reporters.
It was the first fatal shooting in the West Bank since mid-June, when a police officer was killed, and the most lethal attack in the West Bank in four years, when a suicide bombing killed four people at a settlement.
"Security was stable for the past few years and we hope this will not cause any deterioration," Col Leibovich said.
On its website, the Izz al-Din Qassam Brigades, Hamas's military wing, declared "its full responsibility for the heroic operation in Hebron".
Earlier, Hamas spokesman Sami Abu-Zuhri said the attack had been "a natural response to the crimes of the occupation".
He said it was also proof of a "failure of security co-ordination" between Israel and the Palestinian Authority. Hamas seized control of the Gaza Strip from the Fatah-dominated PA in June 2007.
Hebron, in which some 500 Jewish settlers live in fortified enclaves amid about 100,000 Palestinians, has long been a flashpoint for violence.
The BBC's Wyre Davies in Jerusalem says there was no warning an attack like this would take place, and the incident is likely to strain negotiations this week.
Palestinian Authority President Mahmoud Abbas and Mr Netanyahu will attend a meeting with US Secretary of State Hillary Clinton in Washington on Thursday in what will be their first direct talks in nearly two years.
Before leaving the West Bank, Mr Abbas urged "Israel not to miss this historic opportunity for peace," saying that "if there is only a 1% chance of achieving peace we will strive for it".
Mr Netanyahu meanwhile said he hoped for "a peace based on recognition, security, stability and economic prosperity between the two peoples that will endure for us and our children".
Both sides have agreed to place a one-year time limit on the direct negotiations, but correspondents say prospects of a comprehensive deal are slim, as serious disagreements exist on the core issues.
-----------------------------------------Jerusalem (CNN) -- Four Israelis -- including a pregnant woman -- were killed Tuesday near Hebron in the West Bank in a shooting for which the militant wing of Hamas claimed responsibility, officials said.
The incident occurred near Bani Naim junction, the largely Palestinian territory where Jews have settled in places like Hebron, Israel Defense Forces spokeswoman Lt. Col. Avital Leibowitz said. The victims were in a car on Route 60, the IDF website said.
Guy Gonen, a paramedic who was one of the first people on the scene, said the car was sprayed with bullets.
More than a dozen bullet holes were found in the left side of the white Subaru station wagon in which they were driving.
The attack comes ahead of direct talks scheduled to begin Thursday in Washington between Israeli and Palestinian leaders -- the first such talks since 2008.
Izzedin Al-Qassam Brigades -- the military wing of Hamas -- claimed "complete" responsibility for the attack, according to a statement on its website.
Abu Obeida, a spokesman for the group, confirmed responsibility for the attack in an interview with the Hamas radio station.
Sami Abu Zuhri, a Hamas spokesman in Gaza, congratulated the attackers, saying the attack was a normal reaction to what he called "the crime of occupation." Hamas, which controls Gaza, opposes direct talks and the continued existence of Israel.
The four killed -- two men and two women -- were from the settlement of Beit Hagai.
IDF forces were searching for the attackers, the IDF website said.
"This is a serious incident," Israeli Defense Minister Ehud Barak said in a written statement. "The IDF and the security forces will do all that is needed to catch these murderers. Israel will not allow any terror element to raise its head and it will collect the price from these murderers and those who sent them. This is an apparent attempt by base terrorists to harm the efforts to move the peace process and to harm the efforts of the talks that are due to begin in Washington."
The IDF spokeswoman said in a phone briefing Tuesday that the army sees this attack as "very severe," and noted that the security situation in that area had been better in the past 24 months.
"For the last two and a half years there has been a long list of easing of measures. The security situation in the area was very stable in the last two years," Leibowitz said.
The incident is a blow to the efforts of Palestinian leaders to prove that they are doing what Israel has most demanded of them -- preventing attacks and providing tough security.
In response to the attack, settlers from a number of settlements in the north of the West Bank gathered near main road intersections and attacked passing Palestinian vehicles, according to Ghassan Daghlas, the Palestinian official in charge of monitoring settlements in the area.
In addition, some settlers were cutting Palestinian olive trees near Burin village south of Nablus, he said.
In Washington, the press secretary for the State Department condemned the attack "in the strongest possible terms" and said that the Palestinian Authority had also condemned the attack.
"On the eve of the re-launch of direct negotiations between Israelis and Palestinians, this brutal attack underscores how far the enemies of peace will go to try to block progress," the press secretary said in a statement. "It is crucial that the parties persevere, keep moving forward even through difficult times, and continue working to achieve a just and lasting peace in the region that provides security for all peoples."
The U.N. special coordinator for the Middle East Peace Process, Robert Serry, issued a statement saying he "is shocked" by the report. "We condemn this murderous act and call for those responsible to be brought to justice." He called on all parties "not to allow the enemies of peace to affect the negotiations about to be launched, and to progress with determination and courage on behalf of both peoples, towards a final settlement."
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