Andrew Testa / Panos Pictures for NBC News
Father Nizar Semaan gives Holy Communion at Holy Trinity church in the Brook Green area of London.
LONDON -- Rana stepped out of church in Baghdad in December 2006 to find an envelope wedged against her car windshield. Inside was a bullet -- a message that meant she and her family were next on an assassin’s list.
They fled the city the next day, leaving behind a business, a home -- everything.
"I didn't like Saddam Hussein, but he didn't bother the Christians," said Rana, 29, after a church service in London. "He was a dictator. When he went, the gangs came from everywhere."
Rana isn’t alone: Bombings, kidnappings and generalized violence unleashed by the 2003 U.S.-led invasion of Iraq that toppled Hussein caused hundreds of thousands of Christians to flee their homeland.
While there is no centralized source of information on the number of Christians who have left Iraq, it is estimated that there were 2 million there in the 1990s. That number has fallen to between 200,000 to 500,000 today, according to church leaders.
Rana, who like others interviewed would not give her last name because of fear for the safety of relatives still in Iraq, is now part of a congregation that worships at Holy Trinity Brook Green, a Roman Catholic church in West London.
The congregants -- Syriac Catholics whose services are conducted in Aramaic, the language spoken by Jesus -- are part of the estimated 2,500 Iraqi Christians thought to live in the U.K.
In a pew near Rana sat Wasseem, a 26-year-old who arrived in the U.K. five months ago. The murder of his friend Rariq haunts him, Wasseem said through a translator. Rariq, also a Christian, was a driver for American forces in Baghdad and was kidnapped on his way to meet Wasseem. Rariq’s dismembered body was returned to his family five days later.
Extremists have stepped up attacks on Iraqi Christians in recent months, threatening the ancient community's very existence. NBC News' Stephanie Gosk reports.
Wasseem received a handwritten death threat himself. Terrified, he decided to stay in his village in northern Iraq, he said. While safe, the predominantly Christian area offered no jobs, and he soon fled the country.
Extremists haven't targeted only individual Christians and their families. On Oct. 31, 2010, gunmen stormed Our Lady of Salvation Church in Baghdad during Sunday Mass, taking more than a hundred hostages. When security forces tried to free those held, the attackers detonated explosives. At least 58 people were killed, including two priests.
Related video: Baghdad church siege has bloody end
A singer at Holy Trinity Brook Green lost her father in the bombing. Rev. Nizar Semaan, chaplain to the Syriac Catholic community in the U.K., knew both of the murdered priests well.
"They were very courageous people. It is not easy to do their job. And not easy to be a martyr," he said.
Andrew Testa / Panos Pictures for NBC News
Iraqi children make up the choir at the London church.
Semaan’s support for Christians who have fled to the U.K. goes beyond the spiritual.
"I try to help them find accommodation, I ask people to help in any way," he said. "I call people to help them find a job."
Semaan said that he and his fellow priests refused to contemplate the extinction of the Christian community in Iraq, despite its falling numbers.
"Christianity can flourish again. It will grow back as an important part of the region," he said.
Warina, who also attends Mass at Holy Trinity, is more downbeat. Like many of her fellow worshipers, she said life for Christians was better under Saddam Hussein.
"Our neighbors were Muslims. Our relations were friendly. We would visit them," said the dentist who fled Iraq in 2007. "Now it is just fighting. There are lots of churches and monasteries and places to worship in Baghdad -- but they are all empty."
This week marks the 10th anniversary of the start of the Iraq War. ITV's John Irvine in Baghdad assesses a country that, 10 years on, remains gripped by the violence of its sectarian divide.
"We love Iraq. It's our country, the origin of Christianity. But it is not safe," she added.
As Christians, Warina said, they are doubly vulnerable -- not only are they a minority, but they are perceived by some as having colluded with the invading American forces.
"After Saddam's death, people turned on Christians because they think the Christians encouraged the Americans to come to Iraq. Month after month, more and more are killed," she said.
Still, Semaan said he thinks a newly elected Pope Francis will act to support his threatened community.
"The pope will see the persecution and he will take care of us. He will not forget the church in the Middle East," Semaan said. "He is not a politician and he has no army, but he has good will and can encourage dialogue and maybe this can bring about a better situation."
Besides, Iraq needs its Christians, Semaan added.
"The Middle East without Christians would be a country without light," he said. "The future would be very dark."
In the ten years since guided bombs brought "shock and awe" to Baghdad, almost 4,500 troops and 130,000 Iraqi civilians have been killed and Saddam Hussein has been captured and executed in a mission that has cost nearly $2 trillion. NBC's Richard Engel reports.