The Chaldean Archbishop of Mosul in northern Iraq, Paulos Faraj Rahho, was seized by gunmen who attacked his car, killing his driver and two guards in the eastern al-Nour district of the city.
UN envoy Staffan de Mistura said in a statement, "It is appalling that these attacks on communities that have lived peacefully together in north Iraq for centuries are continuing."
The abduction, which took place not long after the Archbishop had left Mass at the Church of the Holy Spirit, is the latest in a series of attacks on Iraq's tiny and dwindling Christian population, which makes up around 3 per cent of Iraq's 27 million, largely Muslim, population.
In January, three Chaldean and Assyrian churches in Mosul fell victim to bomb attacks. Islamic extremists have attacked Christians in the country since the US-led invasion in 2003, believing them to be on the side of the coalition forces.
The Chaldean Church, which practises an ancient Eastern rite, is aligned with the Roman Catholic Church and recognises the authority of the Pope.
Pope Benedict has condemned the kidnapping and called on members of the worldwide Catholic Church to "to unite in fervent prayer so that reason and humanity prevail among the authors of the kidnapping, and that Monsignor Rahho is returned quickly to the care of his flock".
Monsignor Rahho told the Vatican-affiliated AsiaNews agency in an interview last November that Christians in Mosul were suffering more than their fellow believers in other parts of Iraq.
"Religious persecution is more noticeable than elsewhere because the city is split along religious lines," he said.
"Everyone is suffering from this war irrespective of religious affiliation, but in Mosul Christians face starker choices."