Islamist insurgents have issued an ultimatum to northern Iraq's dwindling Christian population to either convert to Islam, pay a religious levy or face death, according to a statement distributed in the militant-controlled city of Mosul

The statement was issued by the Islamic State, the al Qaeda offshoot which led the recent lightning assault to capture swathes of north Iraq. It said that Christians who wanted to remain in the "caliphate" that the Islamic State declared recently in parts of Iraq and Syria must agree to abide by terms of a "dhimma" contract - a historic practice under which non-Muslims were protected in Muslim lands in return for a special levy known as "jizya". "We offer them three choices: Islam; the dhimma contract - involving payment of jizya; if they refuse this they will have nothing but the sword," the announcement was issued in the name of the Islamic State in Iraq's northern province of Nineveh and has been distributed and read out in mosques. It said that Islamic State leader Abu Bakr al-Baghdadi, which the group has now named Caliph Ibrahim, had set a deadline for Christians who did not want to stay and live under those terms to "leave the borders of the Islamic Caliphate". "After this date, there is nothing between us and them but the sword," it said. The Nineveh decree echoes one that the Islamic State in Iraq and the Levant, the former name for the Islamic State, issued in the Syrian city of Raqqa in February 2014, demanding that Christians pay the jizya levy in gold and curb displays of their faith in return for protection. The concept of dhimma, governing non-Muslims living under Islamic rule, dates back to the early Islamic era in the seventh century.