Two of the main Palestinian militant groups say they are not bound by the ceasefire agreed between Palestinian and Israeli leaders at a summit in Egypt yesterday.
However, Hamas and Islamic Jihad, who were at the forefront of attacks on Israel during the Palestinian uprising, say they have been observing a de facto truce.
"The announcement... of a ceasefire expresses the position only of the Palestinian Authority," said Mr Mushir al-Masri of the militant group Hamas, which is committed to destroying Israel.
For their part, Palestinians questioned Mr Sharon's commitment to a viable two-state solution, seeing no reason to give up their deep suspicion that he aims to cement Israel's hold on the West Bank and leave them only with smaller, impoverished Gaza.
An Islamic Jihad spokesman, Mr Mohammed al-Hindi, said the summit had brought "nothing new".
Osama Hamdan, the Hamas representative in Lebanon, said Israel did not fulfil Palestinian demands to release prisoners and halt aggression
Yesterday Palestinian President Mr Abbas said the Palestinians agreed to stop attacks on Israelis while Israeli Prime Minster Mr Sharon called a halt to military operations.
It was the highest-level meeting since near the start of the Palestinian "Intifada" in September 2000. Since then, some 3,350 Palestinians and 970 Israelis have been killed.
Emphasising Washington's new commitment to helping peace efforts, Secretary of State Ms Condoleezza Rice hailed "the best chance for peace we are likely to see for some years".
Although no formal ceasefire was signed at the summit, it was widely seen as a step towards talks on a US-backed "road map" for a Palestinian state alongside Israel.
Israel has agreed on a series of goodwill gestures to boost peace, such as freeing 900 of 8,000 Palestinian prisoners.
It would release 500 next week, its Defence Ministry said.