BEIRUT, Lebanon — Iran declared support on Wednesday for the new Syria peace envoy’s cease-fire proposal, joining Turkey in a rare moment of accord between two of the regional powers backing opposite sides in the 19-month conflict that has pitted the Syrian government against an array of armed opponents.

But the Syrian government expressed skepticism that rebels would honor a cease-fire, and the peace envoy, Lakhdar Brahimi, who represents both the United Nations and the Arab League, said a temporary halt to the fighting would constitute only a tiny step toward resolving the conflict, which has left more than 20,000 people dead.

A veteran Algerian statesman who has been on the job for less than two months, Mr. Brahimi has spent the last several days conferring with Middle East leaders about ways to break the Syria impasse. His predecessor, Kofi Annan, resigned in frustration at the end of August after his proposed peace plan slipped into seeming irrelevance.

On Monday, Mr. Brahimi proposed a cease-fire during the three-day Muslim holiday of Id al-Adha, which begins Oct. 26, hoping that a religious reprieve universally respected by Muslims could be the basis not only for a pause in the fighting but perhaps the beginnings of a dialogue in Syria.