Palestinian and Israeli negotiators are turning to U.S. mediators to bridge serious gaps in drafting a common approach to peace negotiations, officials on both sides said on Thursday.

A senior Palestinian negotiator told Reuters the two sides sought U.S. intervention on Tuesday after negotiators failed to resolve differences over a document they hope to present at a conference in the coming weeks in Annapolis, Maryland, that aims to set terms for relaunching peace talks.

Another senior Palestinian official said that when the sides disagreed this week over the terms of an earlier understanding that Washington would adjudicate in disputes over whether peace terms had been met, U.S. officials sent both a written text.

Palestinian officials also said the latest talks had shown that any document would be shorter on detail than they hoped.

Mark Regev, a spokesman for Israel's chief negotiator, Foreign Minister Tzipi Livni, said: "Anyone who thought it would be smooth sailing all the time was deluding himself."

A U.S. diplomatic source said U.S. officials expected to be involved in bridging differences.

Officials on both sides offered differing views on where disagreements lie. The Palestinian negotiator accused Israel of going back on an agreement made with U.S. Secretary of State Condoleezza Rice earlier this week which, he said, called for U.S. officials to judge whether the sides were taking steps to implement the long-dormant "road map" accords of 2003.

But a senior Israeli official responded: "We agreed on that and there is no change."

ROAD MAP

Israel is unlikely to begin meeting its commitments, notably to rein in Jewish settlement, before the conference, and insists any final peace agreement will depend on Palestinians meeting their road map obligation to ensure Israel's security.

Palestinian leaders say they are already doing that. But Israeli officials are skeptical Palestinians can curb militants any time soon and some have voiced concern that U.S. officials, under pressure to show progress before President George W. Bush steps down in January 2009, might conclude otherwise.

"The Americans ... will play a role in bridging the gaps," the senior Palestinian negotiator said.

A senior Israeli official said: "The likelihood us and the Palestinians will be able to complete a joint statement by the end of the month is not very high. It is actually quite low."

Noting that "the Americans have a big interest" in there being agreement at Annapolis, he said U.S. officials would have to step in to help: "Clearly, they will have to do it."

Officials have said Rice may return to the region in just over a week. But Palestinian officials also said their negotiators may also go to Washington for talks before the Annapolis conference, which is penciled in for November 26 and 27.

Rice and Bush have said they hope a peace deal can be reached before the U.S. administration ends in just over a year.

Palestinian President Mahmoud Abbas has been pushing for a firm deadline for reaching a deal next year. But Israel insists any deal must be conditional on a guarantee of its security.

"We believe the Israelis want a veto over implementation of the peace treaty," the senior Palestinian negotiator said.

He said the timeline issue has not been agreed "but the Americans told us they are looking at a flexible target date that would not exceed the end of Bush's term."