When Hossein Ghanbarzadeh Vahedi, a 75-year-old American of Iranian descent, decided to visit relatives in Tehran in May 2008, he took a flight from Los Angeles in the normal way. When he returned home, his means of transport was somewhat less orthodox.

After seven months in which he was prevented from leaving Iran, had his passport confiscated and saw his appeals ignored by the revolutionary courts, Vahedi took matters into his own hands. In a daring escape, he mounted a horse, hired two guides, and began a perilous 14-hour overnight climb across the freezing mountains of north-western Iran into eastern Turkey. After that he took a bus.

On 9 January 2009, Vahedi turned up at the consular section of the US embassy in Ankara and asked for assistance. To the evident astonishment of American diplomats, Vahedi appeared in good health, but for "a few aches and pains" caused by a fall.

Vahedi's previously untold ordeal, and its happy conclusion, is related in a confidential diplomatic cable from the Ankara embassy seen by the Guardian. In it Vahedi, who left Iran during the 1979 Islamic revolution, tells how his sojourn to his parents' graves and ancestral home turned into a nightmare. His passport was confiscated at Tehran airport as he was about to fly home and the Iranian authorities repeatedly refused to return it, he said. There appeared to be two reasons. One was "simple extortion": it was made clear, he said, that $150,000 (£92,000) would facilitate his departure.

Second, Vahedi said, Iranian government officials told him that he should tell his LA-based sons to stop promoting concerts in the Gulf by Persian pop singers that were considered "anti-regime". He replied that his sons were typical "strong, independent" Americans who would do no such thing.

Of the four commonly used illegal escape routes, he opted for the mountain trail into Turkey. "At one point during the 14-hour ride, the escorts had to physically hug him to keep him warm," the cable recounted. "As an inexperienced rider, hours into the climb, Vahedi lost his concentration and fell off the horse, tumbling into the woods. He told [diplomats] that at this point he really believed he was going to die by freezing to death on a mountainside."

Even when he reached the other side of the border, Vahedi's ordeal was not over. Turkish officials declared him an illegal immigrant and ordered his deportation back to Iran. Luckily for him, US embassy officials had a quiet word with the Turkish foreign ministry – and he was allowed to fly home.