Algerian Foreign Minister Mohamed Seddik Benyahia, who played a key role in freeing the U.S. hostages from Iran, was killed with all others aboard in the crash of his plane on a flight to Tehran, Iran announced today.

The official Iranian news agency IRNA said the private plane crashed near the Iran-Turkey border while Benyahia was en route to an official visit to Tehran and "all the passengers and crew on board . . . were martyred."

The IRNA dispatch, said the Tehran Foreign Ministry suspected "the crash was designed in a calculated plot by the Iraqi regime," with whom Iran has been fighting a war for nearly two years.

It said the planned visit had been designed to "further expand and strengthen existing ties between the two countries and find ways to put an end to the Iraqi-imposed war."

It said that an inquiry team of troops and police, and a special envoy of Algerian President Chadli Benjedid went to the scene of the crash to investigate.

Benyahia mediated in the hostage crisis between the United States and Iran and in February 1981 formally handed over the U.S. hostages to U.S. Deputy Secretary of State Warren Christopher at Algiers airport.