MOSUL, Iraq (The Catholic Herald - UK) - Thousands of Christians have fled Iraq's second-largest city after a dozen people were murdered in the worst week of violence against the faithful since the US-led invasion.

Around 4,000 Christians have escaped Mosul in northern Iraq to neighbouring villages, creating a potential humanitarian nightmare as winter approaches. Many left without any possessions after receiving written threats, and militants blew up at least three Christian homes after chasing out the owners. The Iraqi government has sent 2,500 additional police to the city to protect churches.

The refugees now face a bleak winter without any food or shelter in what aid workers are calling a "desperate" situation.

Some 25 families fled in one day last week followed by another 50 the next day. It turned into an exodus after 13 Christians were murdered, including a father and son and a disabled man in his twenties. Most victims owned or worked in shops, suggesting a campaign to break the economic strength of the Assyrian Christian community.The exiles have moved north and east to the villages of the Nineveh Plains, the last stronghold of Iraq's Christian minority. In one Christian village, Qaraqosh, more than 1,000 refugees are now staying in schools and churches.

However, Qaraqosh and the others villages in the area are already overwhelmed with Christian refugees from the fighting elsewhere in the country, and Christian charities are preparing emergency food, medicine and shelter.

Albert Michael of the Assyrian Aid Society charity called the conditions "desperate" and said: "There are convoys of blankets and tents being prepared. Most of the people are being housed in churches and monasteries. Many are outside and it's getting chilly, and they can't stay much longer. The problem is what happens when these people return to their homes? Ultimately most of the people have to return. Conditions are very bad."

Mosul has been home to a Christian population for almost nineteen centuries and is close to the site of Nineveh, the capital of the ancient Assyrians, from whom Iraqi Christians claim descent. But since 2003 the city has become an Islamist stronghold and the Christian population has dropped from 25,000 to 7,000.

In March the body of Chaldean Archbishop Paul Faraj Rahho of Mosul was found in a shallow grave in the city two weeks after he was kidnapped. His three bodyguards died in the ambush on the way back from celebrating Mass.

Iraq's Christians, variously called Assyrians, Chaldeans or Syriacs, speak modern Aramaic, similar to the language spoken by Christ, and were among the first groups to convert to Christianity. The majority are members of the Chaldean Catholic Church, which is in full communion with Rome. The second-largest of the country's five major churches is the Assyrian Church of the East, from which the Chaldeans broke away in the 16th century.

The Assyrian population in Iraq fell from 1.3m in 1990 to 800,000 in 2003, and is estimated at only 400,000 today. Almost 800 Christians have been singled out for murder since the US-led invasion, but the level of violence had decreased until last month.

The latest wave of murders followed protests by Christians against the Iraqi Parliament's decision to remove Article 50 of the country's constitution, which guaranteed political representation for the country's minorities, among them Assyrians, Yazidis and Turkomen. Assyrians held protests all over northern Iraq as well as in Australia, California, Sweden and London.

At the beginning of October Hazim Thomaso Youssif, 40, was murdered outside his clothes shop. Gunmen killed Ivan Nuwya, 15, outside his home the same day, and two days later a disabled shop owner was taken away from his shop and murdered. Then Amjad Hadi Petros and his son were shot dead together at their workplace. Since then at least eight more Christians have been murdered, the latest last Sunday.

Some Christians also fled from Baghdad and Kirkuk. Several groups of Muslim gunmen entered churches in Mosul and ordered the parishioners to leave within 10 minutes, permanently close the churches and never return.At least three homes were blown up by unidentified attackers in the Sukkar district of Mosul, regarded by US and Iraqi security forces as one of the last urban bastions of Al Qaeda in Iraq.

Local people are unsure of who is responsible for the murders. The Sunni Arab Al Qaeda in Iraq are the main suspects but many believe the Kurds are responsible. Mosul lies just outside the Kurdish Regional Government-controlled area but has a sizeable Kurdish population and the KRG lays claim to both the city and the Christian areas to the north. The KRG has strongly denied that Kurds were responsible.

Duraid Mohammed Kashmoula, governor of Nineveh Province, said it had been a "major displacement" and that the violence was "the fiercest against the Christians since 2003".Speaking from Erbil, 50 miles to the east of Mosul, Chaldean Fr Bashar Warda told Christian charity Aid to the Church in Need: "We are afraid that what is happening in Mosul will develop into a massacre." He said that militants were going from house to house telling Christians to leave and that the people in charge of utility and financial services in the city had warned Christian employees to leave after receiving threats of violence. He also said that the Baghdad government's response was "too little, too late".

Archbishop Louis Sako of Kirkuk said the situation was "critical" and called on the US military to do more to protect Christians and other minorities. "We are the target of a campaign of liquidation, a campaign of violence. The objective is political. We believe it is the responsibility of Americans who occupy our country to protect Iraqis. These attacks are not the first. Unfortunately, they will not be the last. Those who carry out the attacks want to either push Christians out of the country or force them to ally with some political projects."

Last Sunday Pope Benedict XVI said: "I invite you to pray for peace and reconciliation as situations cause concern and great suffering... I think of violence against Christians in Iraq and India."