Kerry said there was a limit to Washington's commitment to efforts to broker a peace if the two sides themselves were not willing to move forward.

The Secretary of State declared late on Friday it was "reality check time" as to whether an agreement could be reached. Kerry's comments came after what he described as unhelpful announcements by both the Israeli and Palestinian leadership.

"Regrettably in the last few days, both sides have taken steps that are not helpful, and that's evident to everybody. So we are going to evaluate very carefully exactly where this is and where it might possibly be able to go," Kerry told reporters, while on a diplomatic visit to Morocco.

Kerry, who embarked on a last-ditch effort to save the floundering peace process last weekend, had been due to return to the Middle East on Wednesday, a day after attending the NATO summit in Brussels.

However, he cancelled after both parties made announcements that backtracked on preconditions for talks, placing the already-fragile negotiations in further jeopardy.

'No open-ended effort'

"There are limits to the amount of time and effort that the United States can spend if the parties themselves are unwilling to take constructive steps in order to be able to move forward," said Kerry. "Neither party has said that they've called it off. But we're not going to sit there indefinitely. This is not an open-ended effort… It's reality check time, and we intend to evaluate precisely what the next steps will be."

Palestinian President Mahmoud Abbas on Tuesday signed 15 United Nations treaties and conventions that give his administration greater recognition. An agreement not to sign such documents had been a precondition set by Israel for talks to go ahead.

Earlier, Israel had said it would reissue 708 settlement tenders in the East Jerusalem neighborhood of Gilo. The Israeli government also called off its promised release of 26 Palestinian prisoners under conditions set for the talks by the Palestinians.

A source familiar with the talks told the Reuters news agency that Israeli and Palestinian negotiators were likely to meet, along with US envoy Martin Indyk on Sunday.

rc/crh (AFP, AP, dpa, Reuters)