A demonstration has been held in Iran by thousands of students from Shi'ite Muslim seminaries protesting against a visit to Teheran last week by a group of Americans.

The students marched through the holy city of Qom chanting anti-American slogans.

On Saturday, a bus carrying the Americans was attacked by Islamic militants wielding clubs.

It followed reports in some Iranian newspapers suggesting the visitors were spies.

The attack was condemned by the Iranian government which said the visit was not political.