As the family of Iraqi Christians sat down for dinner, a group of gunmen forced their way into the house. "Ten or 12 men swarmed into my home like bees," the grandmother of the family told The Times. "They ordered us to stand up and raise our hands.

"They put a bomb in the living room ... and forced us outside. About ten minutes later the house was blown up."

This story of violence against Christians is one of many to emerge over the past fortnight from Mosul, a flashpoint city in northern Iraq. At least 13 Christians have been killed in that period and fear of further attacks has prompted 1,200 families to flee to nearby villages, convents, monasteries and even farther afield to Iraq's Kurdish region to the north or to Baghdad in the south.

The Government has pledged to curb the violence, sending 2,500 additional police to the city -- already the focus of a security operation in May that has so far failed to bring results. The extra forces were designed to assure the Christians of the Government's commitment to their security and protection, said Ali al-Dabbagh, the Government's representative.

Nouri al-Maliki, the Prime Minister, has ordered the formation of a committee to investigate the problem. Yesterday the UN expressed concern at the recent violence against Mosul's Christian community.

Some Christians blame al-Qaeda for the attacks while others speculate that Kurdish elements might be involved as part of a political ploy to coerce minority sects into supporting Kurdish parties before forthcoming provincial elections. This allegation is strongly denied by the Kurdish authorities.

The 69-year-old grandmother whose house, a two-storey building with orange trees in the garden, was destroyed blamed Kurdish paramilitaries. "I suspect they were Peshmerga [armed Kurdish fighters] because their Arabic was broken and they looked like Kurds," the woman said. She, her husband, daughter-in-law and three grandchildren have fled to a village outside Mosul after the attack on Saturday. Two other houses in their neighbourhood were also destroyed.

Fuad Hussein, chief of staff for Masoud Barzani, president of the largely autonomous Iraqi Kurdish region, rejected the idea that Kurdish forces had played a part in any violence against Christians in Mosul.

"That is a campaign conducted by Baathists as well as other terrorist elements in Iraq who are trying to sour the good relationship between the Kurds and the Christians," he said.

"Every time there is a campaign against Christians anywhere else in Iraq proper ... they come towards Kurdistan for a safe haven."

Yonadam Kanna, one of only two Iraqi Christians in parliament, said that al-Qaeda or foreign elements with a political agenda were the likely suspects. "Al-Qaeda is targeting everyone in the country, especially non-Muslims," he said.

Mr Kanna met Mr al-Maliki at the weekend to discuss the problems in Mosul. "[The violence] is very well organised," he said.

The house bombing is just one in a string of incidents suffered by the Mosul grandmother, who was too afraid to let her name be published. Her nephew was shot dead in front of his children a year ago and two of her sons have been forced to flee abroad.

"Christians in Mosul cannot leave their house easily. We look like hippies when we go outside because we have to cover ourselves [with a headscarf]," she said. "Christians cannot walk easily in the street. Wherever they find a Christian they would kidnap him and take his money." Targeted attacks against Christians, who comprise only about 2 per cent of Iraq's population, erupted after the US-led invasion in 2003. Churches were blown up and individuals killed, forcing thousands of Christians to leave the country or flee to the Kurdish north. Mosul initially escaped much of the trouble but Christians in the city say that they have also started to suffer in the past year. In February, Paulos Faraj Raho, the Archbishop of Mosul, was kidnapped and killed.

"Things are not so good in Mosul," said Shlemon Wirduni, the Auxiliary Bishop of the Chaldean Patriarch in Baghdad, who is in contact with churches in the city.

"Today is a little better than before because of the arrival of these new government forces," he said. "The families just want peace and security so that they can return to their homes."

Christianity has a long history in Iraq, with Assyrian and Chaldean Catholics prospering in the ancient city of Ninevah, upon which Mosul was built, as well as in the south of the country. Mosul became a melting pot of ethnicities, comprising Arabs, Kurds and Turkmen, including Muslims, Christians and other minority sects.

They co-existed peacefully until the 2003 invasion when al-Qaeda began to ferment a presence in the city.

A number of attempts to bring security to Mosul failed to achieve lasting success, making it one of the most dangerous parts of Iraq, although US forces based there say that attacks have reduced significantly compared with a year ago.

Mosul bears the scars of years of insecurity. House fronts are pitted with bullet holes and cracks from mortar or bomb blasts. Sewage runs in the street and pavements are lined with litter. Unemployment is estimated to be between 70 and 80 per cent, fuelling the insurgency.

General Tony Thomas, the second in command of US troops in the north of Iraq, estimates that there are still thousands of al-Qaeda supporters in Mosul. He puts the number of active fighters in the "high hundreds, under a thousand".

"You can cut that in half by offering real jobs," he said.

Christianity in Iraq:

• Christians have lived in the area that now forms Iraq for about 2,000 years. According to tradition, Christianity was first preached there by St Thomas on his way to India. Mosul is called Nineveh in the Bible
• Before the Gulf War in 1991 their number was estimated at one million. By 2003 they had dwindled to around 800,000
• Tariq Aziz, Saddam Hussein's Deputy Prime Minister, was Christian, and Christians escaped much of the persecution suffered by Kurds and Shias under the Baathist regime

Deborah Haynes in Baghdad and Tim Albone in Mosul
www.timesonline.co.uk