Iran's Supreme Leader, Ayatollah Ali Khamenei, has urged Muslim countries to boycott a planned US-sponsored Middle East peace conference next month.
Ayatollah Khamenei has the final say on all state matters in Iran
He said the aim of the meeting was to bolster Israel's position at the expense of the Palestinians.
The Palestinian president, Mahmoud Abbas, hopes it will kick-start substantive talks with Israel on the creation of a Palestinian state.
But the Hamas movement, which controls the Gaza Strip, opposes the conference.
Because Hamas will not recognise Israel, renounce violence, or accept previous Palestinian agreements with Israel, it has not been invited.
During a sermon at a mosque in Tehran, Ayatollah Khamenei said the Palestinians see the conference as a hoax which will bring them no benefit.
"How could other governments of the region approve of this conference? They should regard it a mischievous deception as well," he said.
"This US-proposed move is in fact an initiative of the United States of America's regime to save the Zionist regime," he said.
He made no reference to Mr Abbas, who will be attending the meeting.
Iran does not recognise Israel and wants the establishment of a Palestinian state with Jerusalem as its capital.
The US and Israel accuse Iran of backing Shia militias in Iraq and sponsoring Hamas and Hezbollah - charges which Iran denies.
At the moment, the summit looks likely to take place in Annapolis, Maryland, in November.