Sharon has also urged Palestinian Authority President Mahmud Abbas to dismantle what he calls radical groups in the Palestinian camp.
"A ceasefire being discussed by the Palestinians will not advance the war on terrorism and is not the solution, and to this we cannot agree," Sharon was quoted as saying during a meeting in Jerusalem with Dutch Prime Minister Jan Peter Balkenende on Monday.
"The more Abu Mazin (Abbas) delays the dismantling of the terrorist organisations, the more trouble he will have doing it in the future," he added.
Sharon's comment is said to put a damper on the expectations of Palestinian resistance groups who are set to meet in Cairo on Tuesday to work out a formal ceasefire with Israel, hoping that the agreement will persuade Tel Aviv to free more Palestinian prisoners.
Hamas, the largest Palestinian group, has respected an unofficial cooling down period after Abbas was elected president of the Palestinian Authority in January, following the death of Yasir Arafat.
But officials of Abbas' mainstream Fatah party, already gathered in the Egyptian capital, said they were pessimistic about the talks' outcome, citing a hardening of the position of Hamas.
Hamas has joined in the pessimism, ruling out a short-term calm with Israel unless "Zionists" stop their aggression against Palestinian people and release all Palestinian prisoners.
Ismail Hania, a Hamas senior official, said the proposed ceasefire with Israel was doomed to fail if Israel refused to release all Palestinian prisoners.
Hamas leader Ismail Hania
Speaking at a rally in Gaza staged by Palestinian prisoners' families on Monday, he said Hamas had stressed the significance of the prisoner issue when it announced its commitment to the truce.
Israel agreed to start withdrawing troops from three West Bank cities on Wednesday, and promised to study a Palestinian request for the release of Palestinians convicted of involvement in attacks on Israel.
The Cairo talks, which include the Palestinian Authority, the mainstream Fatah movement and a dozen other factions, aims to bring the participants closer to Abbas' position.
The meeting is said to be an attempt to unify Palestinian ranks in order to test Israel's intentions and add to the international pressure on it to respond.
"We will work to reach a joint Palestinian programme that is based on the Palestinian national objectives like the right of return and establishing an independent Palestinian state with Jerusalem as its capital," Mahir al-Tahir, representative of the Popular Front for Liberation of Palestine (PFLP), told Aljazeera from Cairo.
"We will spare no efforts to reach a joint programme that is based on the Palestinian national objectives as there would not be a solution to the Palestinian issue without the right of return and establishing an independent Palestinian state," al-Tahir added.
When asked about Sharon's refusal to commit to a truce before holding Cairo's dialogue, he said: "This indicates Israel's unwillingness to achieve peace.
"Israel wants Palestinians to completely surrender; so the Palestinian Authority and the international community have to realise that Sharon does not seek peace.
"Israel wants to create an internal disturbance and a civil war via imposing demands such as disarming Palestinian resistance factions.
"And we say that as long as there is occupation, we will not hand over our arms under any circumstances to defend ourselves," al-Tahir concluded.