(AFP) -- Christians were fleeing Iraq's jihadist-held city of Mosul en masse on Friday after mosques relayed an ultimatum giving them a few hours to leave, the country's Chaldean patriarch and witnesses said. Iraq is home to one of the world's most ancient Christian communities, but their numbers have plummeted as attacks against them mounted after the US-led invasion in 2003, which unleashed a wave of sectarian violence. "Christian families are on their way to Dohuk and Arbil," in the neighbouring autonomous region of Kurdistan, Patriarch Louis Sako told AFP. "For the first time in the history of Iraq, Mosul is now empty of Christians." Before 2003 the city's Christians numbered some 60,000 people, but that dropped to some 35,000 by June this year, Sako said. Another 10,000 fled Mosul after Sunni Islamist militants took control in a sweeping offensive led by Islamic State (IS) insurgents that began on June 9, and has since spread to other parts of northern and western Iraq. A statement dated from last week and purportedly issued by IS warned Mosul's Christians they should convert, pay a special tax, leave or face death. The deadline to leave the city is noon on Saturday, according to the statement. On Monday two nuns and three orphans were released after being held for 17 days in Mosul, Sako said, a development he described as "a glimmer of hope, and a breakthrough". However, his optimism was to prove shortlived. "We were shocked by the distribution of a statement by the Islamic State calling on Christians to convert to Islam, or to pay unspecified tribute, or to leave their city and their homes taking only their clothes and no luggage, and that their homes would then belong to the Islamic State," Sako said. Witnesses said messages telling Christians to leave Mosul on Saturday were blared through loudspeakers from the city's mosques Friday. The patriarch, who is one of the most senior Christian clerics in Iraq, and residents contacted by AFP said Islamic State militants had in recent days been tagging Christian houses with the letter N for "Nassarah", the term by which the Koran refers to Christians. The statement, which was seen by AFP, said "there will be nothing for them but the sword" if Christians reject those conditions. Iraq's Christian community includes Chaldean, Assyrian and Orthodox sects, but it is a shadow of what it used to be - once numbering more than a million nationwide, with upwards of 600,000 in Baghdad alone, there are now fewer than 400,000 across the country.