"We are disturbed by the harassment of Cardinal Sako, the patriarch of the Chaldean church, and troubled by the news that he has left Baghdad," said State Department Spokesman Matthew Miller.

"We are concerned that the Cardinal's position as a respected leader of the church is under attack from a number of quarters," Miller told reporters.

"We look forward to his safe return. The Iraqi Christian community is a vital part of Iraq's identity and a central part of Iraq's history of diversity and tolerance," Miller said.

Sako announced Saturday he would leave Baghdad for the autonomous Kurdistan region.

For several months, Sako has been embroiled in a war of words with a Christian lawmaker, Rayan al-Kildani.

Kildani is the leader of the Babylon Movement, whose armed wing is part of Hashed al-Shaabi -- a network of largely pro-Iran paramilitaries that were integrated into Iraqi security forces in recent years.

In a statement on Saturday, the cardinal condemned the government's "silence" over what he described as a campaign against him by the Babylon Movement.

Tensions have intensified since early July, when President Abdul Latif Rashid canceled the 2013 decree recognizing Sako as head of the Chaldean Church and allowing him to administer the community's endowment.

In response Sako announced he has "decided to withdraw from the seat of the patriarchate in Baghdad," and would instead settle at one of the monasteries in Kurdistan, in Iraq's north.

Miller called the treatment of Sako as a "blow against religious freedom" and said Washington had made its views on the issue "quite clear" to the Iraqi authorities.