US President Barack Obama Wednesday warned Hamas its "senseless slaughter" would not thwart his Middle East peace drive but a row over Israeli settlements clouded the opening of the long-odds talks.

Obama condemned the Islamist group for gunning down four Israelis on the West Bank, billing the attack as a bid to scupper direct Israeli-Palestinian talks here before they even start on Thursday.

"The tragedy we saw yesterday, by terrorists who are purposely trying to undermine these talks, is an example of what we are up against," Obama said, with Israeli Prime Minister Benjamin Netanyahu at his side.

On the eve of the first direct Israel-Palestinian talks for 20 months, Obama gathered regional power brokers for one-to-one sessions and a joint dinner at the White House, putting his personal credibility on the line.

The talks will take place with few of the parties, or outside observers, predicting success amid widespread regional distrust, and with each side retrenching conflicting positions before the bargaining begins.

Netanyahu told US Secretary of State Hillary Clinton late Tuesday that he would not extend a 10-month freeze on settlement building on the West Bank when it expires on September 26, his office said.

But the Palestinians immediately warned that a resumption of settlement construction would mean the end of peace talks.

"The settlements must be halted and continuing them will signal the end of the peace process," Palestinian spokesman Nabil Abu Rudeina told journalists.

In a flurry of high-stakes diplomacy, coming as his domestic popularity ebbs due to the slowing recovery, Obama was also holding separate talks with Palestinian president Mahmud Abbas, Jordan's King Abdullah II and Egyptian President Hosni Mubarak.

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

Obama's remarks were a clear attempt to offer diplomatic cover to Netanyahu following the Hamas attack, and to stop the killings from disrupting painstakingly-laid US plans for direct Palestinian-Israeli talks.

Branding the attack on two couples, including a pregnant woman, as "sensless slaughter," he warned about "extremists and rejectionists who, rather than seeking peace, are going to be seeking destruction."

"But I want everybody to be very clear: the United States is going to be unwavering in its support of Israel's security, and we are going to push back against these kinds of terrorist activities.

"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.

Netanyahu branded the killings "savagery and brutality."

Hamas, which rules Gaza, is opposed to the peace talks and is a rival of Abbas's US-backed Palestinian Authority.

The issues on the table at the US-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.

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

The Quartet of the United States, the European Union, the United Nations and Russia launched a roadmap for peace in 2003 that calls for a Palestinian state living alongside a secure Israel.

Top level talks in search of the elusive peace deal broke off in 2008 when Israel invaded the Palestinian Gaza Strip to halt militant rocket fire on its south.

Huge issues -- many unresolved since the creation of Israel in 1948 -- remain on the table including the status of Jerusalem, claimed by both sides as their capital, and the fate of Palestinian refugees chased from their lands.

(Source: AFP)