The Russian-built Tupolev 154 aircraft caught fire after a tyre burst on touching down at the shrine city of Mashad. First reports suggested 80 of the 148 people on board had been killed, but this figure was later downgraded by the countries' civil aviation organisation. The plane, operated by Iranairtours, was en route from the southern port of Bandar Abbas. Initial reports suggested that many of its passengers were pilgrims visiting the tomb of Imam Reza, one of Shia Islam's most revered figures, who is buried in Mashad, about 620 miles from Tehran.

Iranian state television showed the charred jet beside the runway as firefighters tackled the blaze. Rescue teams carried out corpses covered in blankets. A gash could be seen in the middle of the fuselage, while the cockpit and rear appeared largely undamaged. Officials said accident investigators were at the scene.

Airline safety has become a sensitive issue in Iran following a spate of crashes that have killed hundreds of people in recent years. The country's rulers blame US sanctions prohibiting the sale of Boeing and Airbus aircraft to Iran. The embargo has forced Iran to buy ageing Soviet-made planes and to scour the black market for parts for older US-built craft bought before the 1979 Islamic revolution.

Many of the country's worst air disasters have involved Soviet-made models. Three crashes involving such planes killed more than 400 people in 2002 and 2003.

An incentive package proposed by the UN security council to settle the dispute over Iran's nuclear programme offers to lift the restrictions to allow it to buy US and European civilian airliners. That offer now appears in jeopardy after Iran this week ignored a UN deadline to suspend uranium enrichment in exchange.

However, the latest crash could renew pressure on the Iranian government to tackle airline safety.Last December there was an outcry after a US-made Hercules military transport plane crashed into a block of flats in Tehran, killing all 94 people on board and 22 on the ground. The crash provoked criticism in Iran's normally pliant media amid claims that fears about the plane's safety had been dismissed.

Earlier this year the head of the revolutionary guards and 10 other senior officers were killed when a Falcon jet crashed near Orumiyeh, in north-west Iran. Iran's worst air disaster occurred in February 2003 when more than 270 revolutionary guards were killed after an Ilyushin-76 crashed in the south-east of the country.