The favourite in the race to become the next archbishop of Canterbury has denounced the west's "morally tainted" war against terrorism in Afghanistan.

The archbishop of Wales, Rowan Williams, has condemned the "confused" US-led bombing campaign in Afghanistan, arguing that it was morally equivalent to the terrorists it sought to defeat.

"It is just possible to deplore civilian casualties and retain moral credibility when an action is clearly focused and its goals are on the way to evident achievement," he writes in a book to be published later this week.

"It is not possible when the strategy appears confused and political leaders talk about a war that may last many years."

Dr Williams is tipped as the favourite in the race to succeed Dr George Carey as archbishop of Canterbury when he retires from the post in October.