Formed by the Syriac Catholic, Syriac Orthodox and Chaldean Catholic churches, the Nineveh Reconstruction Committee is trying to encourage thousands of Iraqi believers back to the Nineveh Plains.
Syriac Orthodox Archbishop Alshamany said: "Today we are truly a united Church - Syriac Orthodox, Chaldean and Syriac Catholic - united in the work of rebuilding these houses on the Nineveh Plains and in restoring hope to the hearts of the inhabitants of these villages and inviting those who have left them to return."
Recently, Catholic charity Aid to the Church in Need (ACN) estimated 12,000 homes damaged by IS could need to be rebuilt - at a cost of more than £160 million.
Syriac Catholic Archbishop Mouche said: "I would like to invite the Christians of the Nineveh Plains to return to their homes and resume living in their villages, in order to bear witness to Christianity.
"Today we join together to demonstrate that we are united in our wish to accelerate this operation as rapidly as possible, and that it must start as soon as possible."
The Committee was unveiled at the Chaldean Archdiocese of Erbil, where many of the 100,000 Christians displaced by the IS invasion in August 2014 fled to.
Syriac Orthodox Metropolitan Sharaf said: "We are the roots of Christianity. We must remain in our country. We must remain as witnesses to Jesus Christ in this country, in Iraq and especially in the Plains of Nineveh.
"This task of rebuilding all the houses in those villages where ISIS has destroyed everything is truly an enormous challenge. Thank you in advance to all those who will help us."
ACN says it will be following closely the Committee's initial operation and, throughout, it will be helping raise financial support.
Top picture: Archbishop Timothaeus Mosa Alshamany, Archbishop Yohanna Petros Mouche, Father Andrew Halemba, Metropolitan Nicodemus Daoud Matti Sharaf, and Bishop Mikha Pola Maqdassi.