US Secretary of State Condoleezza Rice landed in Israel Thursday to "continue to work" on the Israeli- Palestinian peace process, but the White House admitted that it was unlikely the sides would meet their self-imposed deadline.

"We do not think that it's likely that it would happen before the end of the year," White House spokeswoman Dana Perino said, in the first admission by the Bush Administration that that the goal of reaching a deal by the end of 2008 would not be successful.

Rice, who arrived in the region ahead of a crucial briefing in Egypt on the peace process, said en route to Tel Aviv elections in Israel early next year were a "constraint on the ability of any government to conclude what is the core conflict, or core issue of conflict, for Israel and the Palestinians and has been for 40 years."

But she did not completely rule out an agreement, saying that "I think we can sustain momentum. ... I think they can continue to work, as the government has made clear they intend to do. We'll see where they are at the end of the year."

The briefing, to be held Sunday in the Egyptian resort of Sharm el- Sheikh, will be attended by the "Quartet" of international peace sponsors, who will hear Israeli and Palestinian negotiators tell them what has been achieved in the talks since they were launched at a high-profile summit in Annapolis, Maryland one year ago.

They will also be told what obstacles remain and what still needs to be done, Israeli Foreign Ministry spokesman Yigal Palmor said.

Palmor said Foreign Minister Tzipi Livni, also Israel's chief negotiator, was not counting on the Quartet briefing producing any kind of joint document summing up the state of the talks.

Although Israeli Prime Minister Ehud Olmert and Palestinian President Mahmoud Abbas pledged at the US-convened Annapolis summit to try and forge an agreement by the end of 2008, Israeli and Palestinian officials have already conceded that this deadline will not be met.

Abbas said so publicly in Amman earlier this week, admitting that "frankly speaking there will be no comprehensive solution before the end of 2008."

He added there was also "no possibility for working out a partial agreement, because we seek a comprehensive accord."

The Annapolis talks have been bogged down over a lingering dispute over whether Jerusalem, a key deal-breaker, should be included in a treaty now or left to be resolved later.

The early elections in Israel, sparked by Olmert's September 21 resignation amid corruption charges, further complicated the efforts to reach a deal before US President George W Bush leaves office on January 20.

Although he has resigned, Olmert has vowed to continue the Annapolis negotiations as the head of a transitional government. But all main contenders in the upcoming Israeli election say he now lacks the legitimacy to sign a deal.

But making such a deal unlikely anyway is Abbas' rejection of Olmert's proposal to postpone a settlement on the highly-sensitive issue of Jerusalem, while formulating a solution to other key bottlenecks of the Israeli-Palestinian conflict, including borders and refugees.

State Department spokesman Sean McCormack denied reports that Rice planned to place a bridging proposal on the table during the Quartet meeting in Sharm el-Sheikh.

Arriving on her four-day trip to the region in the early afternoon, her eighth since the Annapolis summit, Rice met Olmert in Tel Aviv before heading to the nearby coastal town of Herzliya Pituah for talks and dinner with Livni at the residence of US Ambassador James Cunningham.

On Friday morning she is to hold more talks with Israeli officials in Jerusalem, before travelling to the West Bank city of Ramallah where she is to meet Abbas.

Rice is also scheduled to fly over to Jordan on Friday night to dine with King Abdullah II, and return to Jerusalem, from where she is to head to Sharm el-Sheikh on Saturday afternoon.

According to the Israeli Ha'aretz daily, Rice wants to return home from Sharm el-Sheikh with some form of achievement that would prove to the world that all of her efforts were not wasted.