JERUSALEM, (Reuters) – 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 today.

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.

Israeli settlers

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.

Yesterday’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.