The conference was first proposed by U.S. President George Bush and subsequently approved by the Middle East Quartet, comprising the United States, United Nations, the European Union, and Russia.
"How can Islamic countries possibly participate in this event when the Palestinians describe this conference as a sham and do not intend to attend it?" he said at a religious meeting in Tehran.
He said all Islamic countries should treat the conference as a deception, and a stratagem by the Americans.
Iran's supreme leader said the Americans are attempting to "impose their will on the Palestinian people" and "save the Zionist regime [Israel]."
The meeting in the U.S. aims to produce an Israeli-Palestinian declaration outlining principles for a peace settlement. However, the two sides have very different visions of such a document.
The Palestinians want a detailed agreement specifying each party's commitment on key issues, including future borders, the status of Jerusalem, Palestinian refugees, and Israeli settlements, while Israelis want a more general guideline, preferably a declaration of intentions.
Islamist militant group Hamas warned on Friday that Palestinians would be pressured to make concessions at the conference, and that it could "bring great losses, not only for the Palestinian cause but the entire Arab and Muslim world." The group has not been invited to the talks.
Prospects of a peace settlement between Israel and the Palestinians were severely damaged in June, when Hamas, considered a terrorist organization by Israel, seized control of the Gaza Strip from the pro-presidential Fatah movement, leaving Palestinian President Mahmoud Abbas and his forces in control of only the West Bank.
The United States would like other key Arab states to attend the conference, but many Arab nations remain skeptical and have demanded more details.
