West Bank attack overshadows new Middle East talks
Palestinian security forces have mounted a huge operation in the West Bank to catch the killers of four Israeli settlers shot on Tuesday.
Dozens of members of the Islamist movement Hamas, which said it carried out the attack, have been arrested.
The killings came ahead of Thursday's talks in the US between Israeli and Palestinian leaders - the first direct negotiations in almost two years.
Officials are gathering in Washington for discussions.
US, Palestinian and Israeli officials have said they will not allow the attack, near Hebron, to undermine the talks.
UN Secretary General Ban Ki-moon condemned the killings as a "blatant attempt" to undermine the forthcoming negotiations.
In an overnight sweep, dozens of people linked to Hamas were arrested while Israeli forces sealed off parts of the occupied West Bank and searched villages near Hebron.
Hamas legislator Omar Abdel-Razek said 250 Hamas members had been detained by midday on Wednesday, in an act he labelled treason.
On its website, the Izz al-Din Qassam Brigades, Hamas's military wing, declared "its full responsibility for the heroic operation in Hebron".
The attack took place after dark on Tuesday 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.
Hundreds of people attended a funeral for the four in Beit Haggai, a settlement near Hebron where two of the victims lived.
Palestinian Prime Minister Salam Fayyad has vowed to prevent a repeat of such attacks.
Earlier, Hamas spokesman Sami Abu-Zuhri said the attack had been "a natural response to the crimes of the occupation".
Israeli settlers group the Yesha Council said it would restart construction in the West Bank in protest at the attack, in defiance of a government freeze on new building in West Bank settlements.
Israeli Prime Minister Benjamin Netanyahu said there were no plans to extend the partial freeze on new settlement construction in the West Bank.
His office said on Wednesday that he had said this to US Secretary of State Hillary Clinton during their meeting on Tuesday, AFP news agency reported.
The talks, hosted by the US, seek to reach agreement on the core issues dividing the Israelis and Palestinians, including the status of Jerusalem, Israeli settlements within the West Bank and the borders of the future Palestinian state.
Security is another key issue, with Israel insisting that a Palestinian state be demilitarised with an Israeli presence along its eastern side.
The Palestinians argue that Israeli security will be best served by having a state of their own with as many of the attributes of a normal government as possible.
Palestinian Authority President Mahmoud Abbas is weakened by the bitter feud between his Fatah party and the Hamas movement. Hamas, which controls the Gaza Strip, is bitterly opposed to the negotiations and has been excluded from them.
Both sides have agreed to a one-year time limit on the direct negotiations, but correspondents say prospects of a comprehensive deal are slim, as deep disagreements on the core issues remain.
When they meet US Secretary of State Hillary Clinton on Thursday, Mr Abbas and Mr Netanyahu will be in the same room for the first time in almost a year.
In preparation for the talks, President Barack Obama is to meet the two leaders individually on Wednesday. Mr Obama is also scheduled to meet King Abdullah of Jordan and Egyptian President Hosni Mubarak.
In order to mark the relaunch of direct talks, the US president will host a working dinner on Wednesday evening with all visiting leaders, Mrs Clinton and UN Envoy Tony Blair.
US envoy George Mitchell - whose shuttle diplomacy helped bring Mr Netanyahu and Mr Abbas to the negotiating table - said the goal of reaching a deal within a year was intended to counter the sense that the process was never-ending.