A Russian-made Iranian airliner crashed and exploded in farmland 75 miles northwest of Tehran today, killing all 168 people aboard, after an apparent engine fire.

The Tupolev 154M of Caspian Airlines came down near the city of Qazvin about 15 minutes into the flight bound for Yerevan, Armenia. The crash was the third involving an Iranian Tu154 in seven years.

People on the ground said that the Caspian jet, a later version of the medium-range Soviet workhorse of the 1970s, descended with fire coming from one of its three tail-mounted engines. The pilots appeared to be looking for a landing spot and had lowered the undercarriage when it suddenly plunged, gouging a long trench, and exploded.

“I saw it when it was just above the ground. Its wheels were out and there was fire blazing from the lower parts,” said Ablolfazl Idaji.

The crew did not have time to report their predicament to air traffic control, Iranian authorities said.

Among the 153 passengers and 15 crew were eight members of Iran’s national youth judo team.

Relatives and friends gathered at Yerevan airport, where a notice on a wall listed the names of those who were on board. Iran is home to thousands of ethnic Armenians. Six Armenian citizens and two Georgians were on the flight. The others were Iranian nationals, about 30 of them of Armenian origin, officials said.

President Ahmadinejad issued a statement expressing condolences for the deaths and urging a swift investigation of the cause.

Tehran blames US sanctions for the many crashes that have afflicted its civilian and military aircraft over recent decades. Caspian Airlines is an Iranian-Russian joint venture, however, founded in 1993, which uses only Tupolev 154s. Their maintenance is not affected by the US embargo — but ageing Russian jets suffer from widespread use of bogus spare parts bought on the black market for a fraction of the cost of genuine ones.

There was no immediate indication of what went wrong aboard the Tupolev, which would have been nearing its cruising altitude on its way to Yerevan, but the flight recorders are likely to be retrieved and should shed light on the question. The long trench at the crash scene suggested that the aircraft did not fall vertically but was still in forward motion when it came down, possibly in an aerodynamic stall.

The crash is the third major air disaster in the past seven weeks, after an Air France Airbus went down over the Atlantic near Brazil on June 1, killing 228 people, and a Yemenia Airlines Airbus crashed off the Comoros Islands on June 30, with 152 deaths.

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