WASHINGTON — Iran will not participate in peace talks on Syria that are to be held this month in Switzerland, a senior State Department official said Friday.

“No, they’re not coming,” said the official, who cannot be identified under the department’s protocol for briefing reporters.

Iran, a staunch supporter of President Bashar al-Assad of Syria, has been sending arms and members of its paramilitary Quds Force to help in his government’s military campaign against the opposition.

Along with other Western nations, the United States has said that Iran should not have a formal role when the peace conference opens on Jan. 22 unless Tehran accepts that the goal is to work out arrangements for a transitional governing body that would run the country if Mr. Assad could be persuaded to give up power.