The Palestinian Islamist group Hamas claimed responsibility for killing four Jewish settlers in the West Bank in an attack that blighted a Middle East peace summit before it even began in Washington Wednesday.
Declaring war on the talks promoted by U.S. President Barack Obama as he prepared to host a White House banquet with Israeli and Palestinian leaders, the Hamas militants -- backed by Iran -- said Tuesday's killings were just the first phase.
This attack is a chain in a series of attacks, some have been executed, and others will follow, said Abu Ubaida, a spokesman for the armed wing of Hamas.
Palestinian leaders committed to the peace process joined Israel and the United States in condemning the attack and said direct Palestinian-Israeli negotiations, suspended for 20 months but due to resume this week, would not be derailed.
Hamas, which controls the Gaza Strip, opposes the peace talks and is not taking part. It says Western-backed Palestinian President Mahmoud Abbas, who controls the West Bank, is a traitor for talking to the Israelis about a peace deal.
Jewish settlers in the West Bank said the killings displayed the folly of trying to make peace with the Palestinians.
Obama is staking precious political capital on the drive to resolve a conflict now over six decades old, and the Washington talks were engineered by his Middle East envoy George Mitchell.
This kind of savage brutality has no place in any country under any circumstances, U.S. Secretary of State Hillary Clinton told reporters in Washington as she met Abbas and Israeli Prime Minister Benjamin Netanyahu.
Abbas, who was due to dine with Obama and Netanyahu ahead of the talks, condemned any operation that targets civilians, Palestinians or Israelis.
We are not looking for excuses not to move forward. We want to move forward in peace, and we hope that no one else is looking for excuses, said Mark Regev, Netanyahu's spokesman.
The four Israeli settlers, two men and two women, one of them pregnant, were shot dead after nightfall on the busy Highway 60 close to the West Bank city of Hebron. The road is used by both Palestinians and Israeli settlers.
Hamas's armed wing, Izz el-Deen al-Qassam, said in a statement it took full responsibility for the heroic operation in Hebron.
Its claim confounded recent Hamas signals that it would deter militants from resuming attacks on Israel of the sort that triggered the Jewish state's military assault of the winter of 2008-09 in which 1,400 Palestinians and 13 Israelis were killed.
Abbas said the Highway 60 attack cannot be considered an act of resistance after Hamas itself has stopped resistance from the Gaza Strip and gone after those who carry it out.
This opened the question of who authorised the killings, and whether Hamas was united behind the attack or was now divided.
The United States and allies in the search for a Middle East settlement had urged all parties to refrain from any action that might disrupt direct negotiations.
But Israelis and Palestinians predicted that opponents of peace would try to derail talks with bloodshed, as in the past.
Netanyahu was quoted by a spokesman as saying the killings proved there must be no compromise on Israeli security demands.
This criminal murder proves again the need to stand firmly on Israel's stringent security demands, and there will be no compromise on them, Nir Hefez told reporters in Washington.
Netanyahu had ordered security forces to act without political limits to catch the murderers and react aggressively, he said.
Some Israeli settlers live in a tiny enclave inside Hebron amid Palestinian residents, under the close protection of Israeli army forces. Israeli army sources said all four victims were Israelis from the nearby Beit Haggai settlement.
Israeli settlements in the occupied territory are judged illegal under international law. One Hebron settler leader urged Netanyahu to abandon the delusion of talks, and a settler statement said construction suspended by Netanyahu 10 months ago to facilitate negotiations would restart immediately.
Abbas has said any resumption of Jewish building on occupied land would end the negotiations.
Tuesday's attack was the most lethal in the West Bank in four years, the army said. In a Palestinian uprising from 2000 to 2007, some 540 Israelis were killed in suicide bomb attacks and more than 4,000 Palestinians were killed by Israeli forces.
Hamas spokesman Aub-Zuhri said Tuesday's attack was proof of a failure of security coordination between Israel and the Palestinians.
This was a reference to the Western-backed Palestinian Authority under Abbas, whose U.S.-trained forces are credited with suppressing militants in the West Bank but not Gaza.
Obama's dinner with Netanyahu and Abbas Wednesday was also due to include Jordan's King Abdullah and Egyptian President Hosni Mubarak, expanding the dialogue to two influential Arab neighbours who have made peace with Israel.
The talks are his riskiest foray into Middle East peacemaking -- securing a lasting deal has eluded half a dozen U.S. presidents.
(Reporting by Jeffrey Heller, Alister Bull in Washington, Tom Perry and Mohammed Assadi in Washington, Allyn Fisher-Ilan in Jerusalem; Editing by Ralph Gowling)