One of the oldest Christian monasteries in the world is being used to shelter Christians fleeing persecution by Islamic State in Erbil, Iraq.

The Mar Mattai monastery, which sits about 20km from Mosul, is currently being protected by the Kurdish military, despite being so close to the city that fell to ISIS militants in June of last year.

According to Christians seeking refuge in the fourth century building, hundreds fled to the monastery in the wake of ISIS' attack on Mosul. Many have since left, however, and they told Stripes.com that only a few families remain.

"Every day more people go," 28-year-old Basman Sofia, a Syrian Orthodox seminary student working at the monastery told the website.

He and the few clergy that remain have stayed to minister to Christians living in nearby villages.

The Red Cross is providing some aid to the people living at Mar Mattai, and one woman said that they are not afraid of the possibility that militants could attack. "My God will protect me," she said.

One of the monks earlier this year said he was determined to stay. "We can see the battles and the air strikes from here in front of us, especially at night," said Yousif Ibrahim.

"The sky lights up at night, but we of course are not scared. God protects us."

Mosul was one considered the heartland of Iraq's Christian population, but was overrun by Islamic State jihadists on 10 June, 2014. Upon capturing the city militants issued an ultimatum to Christians, telling them to convert to Islam, pay a tax or flee. Those who refused to comply were murdered, and there are now believed to be no Christians left in the city.

ISIS has declared ancient relics to be idolatrous, and has destroyed many religious sites in Iraq and Syria. Militants have also released images of Christian paintings and statues being destroyed, and reports claim that the Mar Gorgis monastery north of Mosul has been used as a female detention centre, while other ancient churches in the city have been used as slaughterhouses.

There is therefore a siginificant concern that the Mar Mattai monastery may also be targeted.

Speaking to Catholic News Agency in June, however, the Chaldean Archbishop of Erbil, Bashar Warda, said ISIS will not destroy the faith of his community.

"They've destroyed walls and historical sites, but they were unable to destroy the faith of the community," he said.

"And that's the good news, that our people are strong enough to leave everything behind and just stay Christians."