The Afghan-born US Ambassador to the United Nations, Zalmay Khalilzad, has signalled that he will run for the presidency of Afghanistan in elections next year.

Mr Khalilzad is a senior figure in the Bush administration who served as ambassador to Kabul before becoming ambassador to Iraq and then the UN.

He holds US citizenship, is married to an American and is a former professor at Columbia University.

He has fuelled speculation of a run by announcing on Afghan television: "I will resign from my official work in the next few months and start a private business."

Asked if he would stand for the presidency, he replied: "I have said earlier that I'm not a candidate for any position in Afghanistan, but I am at the service of the Afghan people."

Sources close to Mr Khalilzad within the Afghan establishment insist that he is considering a run for the presidency and has been putting out feelers to political factions within the country.

"He is under pressure to stand from within Afghanistan," said one source. "His comments are genuine in that he will come to Afghanistan and work in the private sector, but he will reassess towards the end of this year whether he has a chance to take the presidency."

Mr Khalilzad is rumoured to have long had his eye on replacing President Karzai, the man he picked to become Afghanistan's first president in 2004.

Mr Khalilzad's supporters are alleged to have sounded out Pashtun tribal chiefs in the south as well as figures within the Northern Alliance, which now calls itself the National Unity Front.

The popularity of President Karzai has waned as disquiet at government corruption and the resurgence of the Taliban has been felt across the country.

Mr Karzai has become increasingly critical of the international community in an apparent attempt to bolster support at home, most notably by attacking Britain and blocking Lord Ashdown, the British diplomat, for the position of UN envoy in Kabul.

The Afghan president let slip his own intention to stand for re-election this week.

Following his return from the Nato conference in Bucharest on Sunday, Mr Karzai said: "I want to complete the work that I started - if they vote for me."