Three Britons who were killed in Iraq were making a pilgrimage carried out by thousands of Shia Muslims every year, despite risks posed by the volatile country.
Shia Muslims gather in the holy city of Karbala for anniversaries
Yousif al-Khoei is a director of the al-Khoei foundation, the largest Shia organisation in the UK.
He believes up to 5,000 Shia Muslims from the UK visit holy sites in Iraq every year.
"There are two different reasons why people go to the shrines in Iraq," he said. "Some go while they are in Iraq visiting family and so will go a number of times.
"But many Iraqis will combine visiting many shrines on one trip. They would collect life-time savings to do this and it would be very significant for them to be in this spiritual atmosphere."
He said Shia Muslims had a "great emotional attachment" to their imams.
The visiting the shrines is not a religious obligation, in the same way as visiting Mecca is, but is regarded as significant by Shia Muslims and something many would hope to do.
Such visits take place despite UK Foreign Office warnings against travel to Iraq. A spokeswoman said the office had warned against non-essential travel to the country since the invasion of Kuwait in 1990.
The Britons who died were reportedly shot when their minibus neared a checkpoint in Baghdad as they headed towards the airport after their pilgrimage.
The cities of Najaf and Karbala see thousands of visitors as they are home to some of the most sacred shrines of the Shia branch of Islam.
They are also leading centres for scholars of Islamic theology.
Karbala, 80 kilometres (50 miles) south of Baghdad, is revered as being the site of the death of the Shia martyr Imam Hussein, a grandson of the Prophet Muhammad.
Imam Hussein died 1,325 years ago, killed in battle as he fought for the right to be caliph or successor to the Prophet. Shias believe he was thus denied the leadership of Muslims.
Shia pilgrims visit his tomb, which has a gilded dome and three minarets, and is the central building in the city.
Hussein's father, Imam Ali, is buried at Najaf, 190km south of the capital.
Mr Khoei used to live in Karbala and Najaf and says both their economies are centred on receiving thousands of visitors a week.
Karbala and Najaf are spiritual places for many who visit
There are two key times for pilgrimages - Ashura, commemorating the death of Hussein, and Arbaeen, 40 days later.
Many Shia Muslims were banned from visiting the shrines under Saddam Hussein's regime and at one time Karbala was "razed to the ground", Mr Khoei said.
He added there were still dangers from different groups, including ones who believed visiting shrines was sinful.
His uncle, Abdul Majid al-Khoei, was one of two Muslim leaders killed outside the Imam Ali Mosque in 2003.
Abdul Majid al-Khoei was a senior cleric working with coalition forces and he was expected to have taken part in a conference on Iraq's future after the war.
Mr Khoei believes Iraq's recent security problems have put Shia Muslims off and "numbers have dropped."
"But last year I was there and saw quite a lot of foreign pilgrims, including some from the UK," he said.
'Peace and tranquillity'
He said people prayed and reflected at the sites.
"There's an aura of peace and tranquillity. You try to consider your sins and make a new start," he said.
He said there were UK-based travel companies offering tours of religious sites, but believed most now travelled in community groups or independently.
Mohammed Bhojani, a member of the Muslim Council of Britain's community working committee, believes UK-based Shia Muslims who visited mainly took tours from Dubai, Kuwait or Jordan.
However, he believed most took the Foreign Office advice and didn't go.
He pointed out the Britons who died had been attacked in Baghdad, whereas in the south the majority of people were Shia and the region was considered "relatively safe" for them.
Mr Bhojani, 42, made his own trip to the sites as a child.
"I went many years ago, when I was very young, about eight or nine," he said. "My visit was very nice, very spiritually fulfilling."
He said Shia Muslims would learn the history and importance of saints and imams as they grew up, so visiting the sites would be very significant.
"It is similar to a Catholic visiting Lourdes or a Christian visiting Bethlehem."
However, he added a visit to Iraq "does not take precedence over a visit to Mecca or Medina".
BBC Middle East analyst Roger Hardy said that despite relative security in some parts of Iraq, there were still frequent bombings, killings and kidnappings and that Iraqi civilians were among those targeted.
"The violence has not spared the two sites especially revered by Shias worldwide, the holy cities of Najaf and Karbala," he said.
"The killing of British Shia pilgrims, as they were returning to Baghdad from the holy cities, suggests militants may regard all Shia as targets, whether Iraqi or non-Iraqi."
Meanwhile, Ibrahim Mogra, the chairman of the Muslim Council of Britain's Mosque and Community Affairs committee, said thousands of Britons made the pilgrimage to Mecca each year.
"Every able-bodied Muslim is expected to make the trip, as long as they leave people they are responsible for at home looked after. The Hajj pilgrimage is one of the duties, alongside prayers, fasting and charity."
He added that people of all traditions and faiths should be "safe and secure" to visit holy sites and carry out their pilgrimages.