A 41-year-old Spanish soccer fan who set out to walk to Qatar to attend the World Cup in November has gone missing in Iran, where unrest has erupted in the past few weeks, Spain's foreign ministry has confirmed.

Santiago Sanchez was last heard from on 1 October when he sent friends a picture of himself on the Iraq-Iran border with the caption: "Entry to Iran".

Some Spanish media suggest Mr Sanchez had been arrested by the Iranian authorities and his parents in Madrid told Telecinco TV channel that was the most likely possibility.

"A 99% chance that he is in a prison in Iran, but the (Spanish) embassy has told my daughter that until they go to the prison to see him and have the permission of the Iranian government, they cannot give that news," his mother Celia said.

Police summoned the parents to provide dental records, personal items such as a toothbrush and photos of Mr Sanchez's tattoos, which they will send to Interpol, she explained.

Spain's Foreign Ministry confirmed Mr Sanchez was in Iran and its embassy in Tehran was urgently seeking information on his whereabouts to provide him with consular assistance.

"The embassy is in permanent contact with the Iranian authorities since it was made aware of the disappearance," it said in a statement.

Mr Sanchez is seen here walking through Erbil in Iraq

Iran is facing the biggest protests in the history of its clerical leadership following the death last month of 22-year-old Mahsa Amini, a Iranian Kurdish woman, who was detained by the morality police in Tehran for "inappropriate attire" and died in police custody.

Earlier today, Iranian security forces opened fire on and detained mourners who gathered in Amini's hometown of Saqez, close to the Iraqi border, to mark 40 days since she died.

Miguel Bergado, a close friend of mr Sanchez's and fellow traveller on previous occasions, said he had heard no more of Mr Sanchez since the photograph of him crossing the border.

"He was about to have his passport stamped, pay and enter," he said.

"We are trying to be calm because Santi is an experienced person who respects rules, cultures and borders. He has already been to Iran, it's a hospitable country... but this time it was a delicate moment."

Mr Sanchez hopes to inspire the Spanish team to victory

Mr Sanchez left Madrid in January, travelling across Europe and Turkey, sleeping in a tent, hotels and well-wishers' homes, before entering Iraq.

He told Reuters in Zakho in Iraqi Kurdistan last month that he hoped he might meet the Spanish team and inspire them to victory in the 2022 World Cup.

"If you don't set a date for your dreams, you don't realise them," he said, explaining that the 20 November kick-off date drove him on through extreme heat and uncertainty about his next meal or bed.