Lord Rowan Williams was giving a speech at Cheltenham Literature Festival when he said: "I have people I know who are currently being held in the Middle East, including two bishops in Syria, and I am waiting to find out their fate."
When asked by a member of the audience if the Church should be doing more to condemn Islamic State, he replied: "I couldn't agree more.
"Many have been speaking up and I hope more will. One of the dangers we face at the moment is the rise of a particular kind of religious tyranny in that region, whose results both locally and globally are lessons for us all.
"We cannot turn our backs on that. It is not academic - I am glad there are people speaking out."
The former archbishop did not name the men, although The Daily Telegraph claims it is Bishop Boulos Yazigi of the Greek Orthodox Church and Bishop John Ibrahim of the Assyrian Orthodox Church.
The newspaper says the pair were pulled from their car by gunmen in April last year while travelling in the Syrian city of Aleppo.