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

Wading into a new round of Middle East diplomacy in the face of deep scepticism over his chances for success, 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 launched 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.

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

But big obstacles remain to Obama's quest for a two-state solution that eluded so many of his predecessors.

Militants from the Islamist Palestinian group Hamas declared war on the talks even before they began, killing four Jewish settlers in the occupied West Bank on Tuesday, vowing more attacks and underscoring the threat hard-liners pose to the fragile peace process.

Standing shoulder to shoulder with Obama, Netanyahu said Israel would a seek a peace accord centered around the need to have security arrangements that are able to roll back this kind of terror and other threats to Israel's security.

(Additional reporting by Andrew Quinn in Washington; Allyn Fisher-Ilan in Jerusalem, editing by David Alexander and Will Dunham)

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