A plane carrying 270 people, all military personnel, crashed in southern Iran tonight, killing all on board, the official Islamic Republic News Agency reported.
The plane was on a domestic route from Zahedan, on the Pakistan border, to Kerman, about 500 miles south-east of Tehran, state-run Tehran television reported. It crashed in a mountainous area about 50 miles from its destination, near the city of Shahdad.
The television report said the plane lost contact with the control tower at 5.30pm local time (1400 GMT).
IRNA reported that all on board the plane had died. It said the plane's passengers were all members of the elite Revolutionary Guards.
State television and radio did not offer reasons for the crash and did not address the possibility of terrorism. There was heavy snow in many parts of Iran tonight, including in Zahedan, which hadn't seen snow for three years.
An anonymous official told Tehran television that the military forces had visited the impoverished Sistan-Baluchestan province, of which Zahedan is the capital, for an "important duty." The military corps is seen as a defender of Iran's Islamic regime.
The report said the plane was a Russian-made Antonov airliner. There were no more details available on the crash.
The government issued a statement offering condolences to the families of the victims, television and radio reports said.
Iranians were preparing for an Islamic holiday tomorrow, the feast of Velayat, when Shiites believe the prophet Mohammed appointed his son-in-law, Ali, as his successor.
Tonight's crash was the latest in a string of air disasters in Iran involving mostly Russian-built airliners.
Last December, transportation minister Ahmad Khorram acknowledged that Iran's air industry was suffering under US sanctions and warned there would be more air disasters if sanctions on purchase of US-made planes were not lifted.
He spoke days after the December 23 crash of a Ukrainian An-140 aircraft, which killed all the estimated 46 scientists aboard.
In February 2002, the Russian-made Tupolev Tu-154 airliner, carrying 119 people, crashed into snow-covered mountains not far from its destination of Khorramabad, 230 miles south-west of Tehran.
In May 2001, the Russian-made YAK-40 plane crashed in bad weather in northern Iran killing all 30 people on board, including the then transport minister, the late Rahman Dadman, and seven politicians.
Since the 1979 Islamic revolution, Iran has been forced to supplement its fleet of Boeing and European-made Airbus airliners with planes bought or leased from the former Soviet Union.
Iran has a total of about 80 working passenger planes. About 30 to 40 of those are believed to be Russian-made Tupolovs, 10 Fokkers from the Netherlands, and the rest Airbus and aging Boeings. In the mid-1990s, Iran purchased two or three Airbus planes.