Afghan President Hamid Karzai used a keynote anti-corruption speech yesterday to defend the most senior of his officials to be convicted of graft in years, a move that could anger Western backers who demand more accountability.

The President opened a three-day, anti-corruption conference, which had been billed by diplomats as a sign that Karzai took seriously the West's concern over an issue seen as key to winning popular support against a resurgent Taliban.

Shortly before he spoke, a suicide bomber blew himself up in the capital's Wazir Akbar Khan diplomatic residential district, killing eight people and wounding at least 40, according to the Interior Ministry. The blast took place outside the home of a former vice president, who was unhurt.

Mr Karzai spoke at length about the bribes ordinary Afghans are forced to pay, and rebuked officials who "after one or two years work for the government, get rich and buy houses in Dubai".

However, he also cast doubt on the biggest anti-corruption conviction his prosecutors have achieved in years.

Kabul Mayor Abdul Ahad Sayebi, a Karzai appointee who was sentenced to four years prison last week for corruption and is now free on bail pending an appeal, attended the conference seated toward the front. Mr Karzai pointed him out.

"One very serious caution I want to say. The mayor of Kabul has been sentenced to four years jail. I know the mayor. He is a clean person. I know him," Mr Karzai said.

He said Sayebi had been targetted by enemies for refusing to grant them government land, and gestured to his Chief Justice and Attorney General demanding they look into the case, although he also said Sayebi should still go to jail if guilty.