"We have to be very careful as we are trying to move toward the establishment of a Palestinian state, of actions and statements that erode confidence in the parties' commitment to a two-state solution," Rice told journalists on the journey from Russia.
"Even if the intentions are good and even if the actual events on the ground are intended to produce a certain kind of outcome, this is a very delicate time," she said.
"It's just a time to be extremely careful." Shuttle diplomacy
Rice said she would shuttle between Israel and the West Bank over the next three days to the two sides "narrow differences" over the outline of a joint statement to be presented at the meeting, expected to be held in Annapolis, Maryland in late November.
"The question is will Fatah be strong enough to contain such a powerful 'partner' or will it be just exploited and eroded over time?
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But the US secretary of state played down any expectations of a breakthrough over the document during the next few days.
"I would just warn in advance not to expect that, because this is really a work in progress," she said.
Rice, on her seventh trip to the region this year, on Sunday discussed the land seizure with Ehud Barak, the Israeli defence minister, as well as ways to ease restriction on Palestinians travelling across the occupied West Bank, an Israeli official said.
She then held talks with Ehud Olmert, the Israeli prime minister, and the leaders of Israel's main political parties before having dinner with Salman Fayyad, the Palestinian prime minister in the West Bank government.
But even before she began her meetings, Olmert suggested that an outline agreement was not necessary for the conference to go ahead.
The goal "is to arrive at a joint statement during the international conference, even though the existence of such a statement was never a condition for holding this conference," Olmert said. Public relations
However, Riad Malki, the foreign minister in the Ramallah-based Palestinian government, threatened to boycott the summit over the issue.
"Without a document to resolve this conflict, we can't go to the conference next month," he said.
"Olmert is looking for a public relations conference and one that will allow normalisation with Arab countries," he said. "We will not help him in this."
Israeli and Palestinian negotiating teams have already begun discussing the document which is expected to address "core issues", such as borders, sovereignty over disputed Jerusalem and a solution for Palestinian refugees.
Israel is pressing for a vaguely worded document that would give it more room to manoeuvre, while the Palestinians want a detailed preliminary agreement with a timetable for creating a Palestinian state.