Gunmen on Friday kidnapped Chaldean Catholic Archbishop Paulos Faraj Rahho in the northern Iraqi city of Mosul, police and the church said.
The gunmen also killed three people who were with Rahho, 65, at the time of the kidnapping, which occurred after he ended a Mass in a nearby church, said Iraqi Brig. Gen. Khalid Abdul-Sattar, a spokesman for the Ninevah province police.
An aide to Iraq's Cardinal Emmanuel III Delly, leader of the church, said he did not know who was behind the kidnapping.
"We pray for his release as soon as possible," said Archbishop Andreos Abouna. "This act of abduction against a Christian clergy member will increase our fears and worries about the situation of Christians in Iraq."
Last year's International Religious Freedom Report from the U.S. State Department noted that Chaldean Catholics comprise a tiny minority of the Iraqi population, but are the largest group among the less than 1 million Christians in Iraq.
Since the U.S.-led invasion in 2003, Iraqi Christians have been targeted by Islamic extremists who label them "crusaders" loyal to U.S. troops.
Churches, priests and business owned by Christians have been attacked by Islamic militants and many have fled the country.
Last June, Pope Benedict XVI expressed deep concern about the plight of Christians caught in the deadly sectarian crossfire in Iraq and pressed U.S. President George W. Bush in a meeting to keep their safety in mind.
"Particularly in Iraq, Christian families and communities are feeling increasing pressure from insecurity, aggression and a sense of abandonment," Benedict said at the time.
Iraq's Prime Minister Nouri al-Maliki pledged last fall to protect and support the Christian minority.