Gordon Brown has warned Hamid Karzai that he needs to tackle corruption in Afghan politics to keep international support.

During a meeting at No 10 with UN secretary general Ban Ki-Moon, Mr Brown said: "These are important days for Afghanistan when the president is inaugurated. We will want him to make clear that he is going to take immediate action on corruption."

Mr Karzai's victory was declared on Monday after Afghanistan's Independent Electoral Commission decided to call off this weekend's second-round presidential ballot, which was triggered by his failure to obtain 50% of votes in an election in August which was marred by widespread fraud.

The ballot had effectively become meaningless following the withdrawal from the race on Sunday of Mr Karzai's only remaining rival, former foreign minister Abdullah Abdullah, who claimed the run-off poll would not be fair.

Mr Brown said Britain wanted to see "a corruption-free government, an inclusive government and a government which will tackle the problem of bringing prosperity to the Afghan people".

He said that if Mr Karzai was successful in tackling these issues and building up the Afghan military and police force, "that will allow British and other troops to come home".

He acknowledged that Mr Karzai faced an "extremely challenging" task and said he looked forward to "further indications" from the President about how he would tackle corruption. He also offered his condolences to the UN following the death of its staff in a recent bombing attack in Kabul.

Asked if international aid would be conditional on seeing corruption eradicated, he said: "We'll only give aid to projects we are sure are going to be delivered."

Setting out the actions he expected the President to take, he said steps should be taken over corrupt officials and district officials must be "free of any stain of corruption".

He said: "What we want and what he (Mr Karzai) now wants is action on corruption, building up the Afghan army and police force and showing that he can bring prosperity to the Afghan people by controlling the drugs trade."