British politician and former soldier Paddy Ashdown on Sunday withdrew from the contest to be United Nations' envoy to Afghanistan after Kabul said it favoured a British Nato commander for the post.
Violence in Afghanistan over the past two years has been the bloodiest since US-led forces ousted the Islamist Taliban and there have been calls for a high-level envoy to co-ordinate with the Afghan government and bodies such as Nato and the European Union.
However diplomats say Afghan President Hamid Karzai is wary that a powerful "super-envoy", particularly one from former colonial power Britain, might make his government appear weaker than it already is.
"This job can only be done successfully on the basis of a consensus within the international community and the clear support of the government of Afghanistan," Ashdown said in a statement on Sunday. On Sunday, Afghanistan's Foreign Minister Rangeen Dadfar Spanta said the government favoured either McColl or Turkish politician Hekmat Cetin for the post. Cetin served as Nato's civil envoy for the country in recent years.