The U.S. President Barack Obama also vowed on Wednesday that a deadly Hamas attack in the West Bank "is not going to stop us" in the quest for Israeli-Palestinian peace as he opened a Washington summit to relaunch face-to-face negotiations.

Wading into Middle East diplomacy in the face of deep skepticism over his chances for securing an elusive peace deal, Obama condemned as "senseless slaughter" the ambush that killed four Israeli settlers on Tuesday in the occupied West Bank.

"The message should go out to Hamas and everybody else who is taking credit for these heinous crimes that this is not going to stop us from not only ensuring a secure Israel but also securing a longer lasting peace in which people throughout the region can take a different course," Obama told reporters.

Obama spoke after meeting Israeli Prime Minister Benjamin Netanyahu as he began a series of one-on-one sessions with Middle East leaders attending the U.S.-led peace summit that will culminate on Thursday with the first direct Israeli-Palestinian talks in 20 months.

The summit marks Obama's riskiest plunge into Middle East diplomacy, not least because he wants the two sides to forge a deal within 12 months for the creation of a Palestinian state alongside a secure Israel.

The Palestinians want a state in the occupied West Bank and the Gaza Strip, with its capital in East Jerusalem, whose Old City houses al-Aqsa, Islam's third-holiest shrine, along with the Western Wall, a vestige of Judaism's two ancient temples.

With the clock ticking toward the Sept. 26 expiration of an Israeli settlement construction freeze that could also undermine the talks, Israel's defense minister sounded a conciliatory note about the prospects for sharing Jerusalem, an issue at the heart of the decades-old conflict.

Big obstacles remain to Obama's quest for a two-state solution that has eluded so many of his predecessors. There is also the danger that failure on this front could set back Obama's faltering attempts at winning over the Muslim world as he seeks solidarity against Iran.

Abbas is my partner in peace:Netanyahu

Israel Prime Minister Benjamin Netanyahu Wednesday called Palestinian leader Mahmud Abbas "my partner in peace" and said he was seeking a peace to end the Middle East conflict "once and for all."

But the Israeli leader warned, in excerpts of a statement to be made later at the White House, that "peace must also be defended against its enemies."

"Our goal is to forge a secure and durable peace between Israel and the Palestinians. We do not seek a brief interlude between two wars. We do not seek a temporary respite between outbursts of terror," Netanyahu was to say, according to the excerpts released by Israeli officials to journalists.

"We seek a peace that will end the conflict between us once and for all. We seek a peace that will last for generations. This is the peace my people want, this is the peace we all deserve."

The Israeli prime minister also paid tribute to Abbas.

"Every peace begins with leaders. President Abbas, you are my partner in peace. It is up to us to live next to one another and with one another," Netanyahu was to say.

All five leaders were due to stand together at a potentially awkward White House appearance to make individual statements, before retiring for the dinner also featuring Quartet diplomatic representative Tony Blair.

Netanyahu was also to say that "peace must also be defended against it's enemies. We want the skyline of the West BBank to be dominated by apartment towers, not missiles. We want the roads of the West Bank to flow with commerce, not terrorists.

"We left Lebanon, we got terror. We left Gaza, we got terror. We want to ensure that territory we concede will not be turned into a third Iranian-sponsored terror enclave aimed at the heart of Israel."

"That is why a defensible peace requires security arrangements that can withstand the test of time and the many challenges that are sure to confront us."

The White House said the day of intense presidential engagement was meant to build trust ahead of direct U.S.-engineered Israel-Palestinian talks due to be hosted by Clinton on Thursday.

It insists that a "window of opportunity" has opened up to forge a two-state solution in the Middle East, at a time when Iran's growing influence is threatening to reset the regional political map.

The issues on the table at the U.S.-mediated talks -- the status of Jerusalem, security, the borders of a Palestinian state and the right of return for Palestinian refugees have confounded all previous mediation attempts.

Israel, Palestinians hunt settler attackers in West Bank

Israel sealed off parts of the West Bank on Wednesday while Palestinian security forces arrested scores of Hamas supporters after four settlers were gunned down just ahead of Middle East peace talks.

Furious settlers vowed to flout a moratorium on settlement construction in protest at the attack, as tensions rose ahead of a Washington summit hosted to relaunch talks suspended in 22D8.

Israeli soldiers carried out house-to-house searches in villages in the Hebron area, near the Kiryat Arba settlement where two couples, including a pregnant woman, were killed on Tuesday evening.

Access routes to the city of Hebron were closed by military roadblocks.

"We are operating on a number of different levels since the event took place and will continue to act until we get a hold of the terrorists," military Chief of Staff Lieutenant General Gabi Ashkenazi said as he and other generals visited the area.

Hamas, which claimed the attack, said Palestinian security forces had arrested more than 250 of its members, including relatives of MPs.

A Palestinian official had earlier confirmed the arrest of 50 Hamas supporters. There were no reports of any Israeli arrests.

The Islamist group ruling Gaza accused Palestinian president Mahmud Abbas in a statement from its MPs of "siding with the Zionist enemy and continuing its project to abort and uproot the resistance."

The statement went on to warn "Fatah and its authority of the dangerous consequences of this escalation," referring to Abbas's secular party.

The victims of the shooting were believed to be settlers from the area.