Switzerland played a "positive role" in almost a year of efforts for a prisoner swap between Iran and the United States, Tehran's ambassador to the United Nations told state television Saturday.

"It took almost a year and naturally the government of Switzerland as a facilitating country played a positive role in these negotiations," Gholam Ali Khoshroo said, after Iran released four Iranian-Americans and the US freed seven Iranians it was holding.

"The release procedure is ongoing," he said.