The hard-line Qods newspaper said the threat was delivered in a statement phoned in by an anonymous caller who said he belonged to Fedayeen Islam, or Volunteers for Martyrdom for Islam, which has not been heard from for more than a decade.
The threat was chiefly directed against former hostages Barry Rosen and Bruce Laingen, who have said they would be willing to visit Iran.
Fedayeen was active in fighting the U.S.-backed Shah's regime during the 1960s and the period leading to the 1979 Islamic Revolution that overthrew the Shah. The group was blamed for the 1965 assassination of then-Prime Minister Hassan Ali Mansoor.
In a telephone call to Qods, the devotees of Islam's spokesman specifically referred to a suicide car bombing at the U.S. Embassy in Beirut in 1983 in which 63 people were killed.
The Farsi-language Qods said the Fedayeen "warned that it considers itself duty bound to carry out suicide attacks against Bruce Laingen and Barry Rosen and other individuals associated with the den of spies if they return to Iran."
"The history of the Great Satan's treason and hostility towards the government and people of the Islamic Republic is clear to all," the daily quoted the spokesman as saying.
Militant Islamic students who stormed the embassy and took 52 Americans hostage for 444 days referred to the embassy as the "den of spies."
At a demonstration last week to mark the 19th anniversary of the seizure, the student leaders who seized the embassy invited former hostages to return to Iran.
All but about six of the students who were once zealous supporters of the Islamic Revolution and its leader, Ayatollah Ruhollah Khomeini, are now considered moderates who back President Mohammad Khatami's call for dialogue with the American people.
Several hold key posts in Khatami's administration.
But a new breed of hard-liners clustered around the supreme leader, Ayatollah Ali Khamenei, is opposed to any compromise with the United States. At a rally outside the former embassy last week, the hard-liners burned effigies of Uncle Sam and called for "Death to America!"
Laingen, who as charge d'affaires was the most senior diplomat among the American hostages, said last week he has looked forward to returning to Iran following a new relationship between Iran and the United States.
Rosen, a former press attache at the embassy who now heads the public affairs department of Teachers College at Columbia University, said he also would "be in favor of going back to Iran" at the right time.
The anonymous caller who phoned in the death threat told Qods the group was made up of "youths and combatants who considr it their duty to implement the dictates of Islam."
Relations between Iran and the United States were severed after the embassy seizure. But ties have thawed somewhat since Khatami in January called for more unofficial exchanges to help relations at a grass-roots level.
©1998 CBS Worldwide Corp. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press and Reuters contributed to this report