Mr Brown said a "better form of government" was needed
A new Afghan administration must make tackling corruption a "key priority", UK Prime Minister Gordon Brown has told President Hamid Karzai.
Mr Brown was speaking to Mr Karzai after his rival, Abdullah Abdullah, withdrew from the presidential election citing fraud fears.
Whether the second round of voting went ahead was up to the independent electoral commission, Mr Brown said.
He said Mr Karzai was planning a "unity manifesto" to stabilise the country.
"Our first priority is the safety and security of our troops. We need the infant Afghan democracy to be stable and inclusive," Mr Brown said.
"We have got to have a visible sign that the new administration is tackling corruption, we have got to know that they are going to build up the local elements of popular rule.
"We have got to know that they are going to bring greater prosperity to the Afghan people and they have got to have an army and police that is capable of keeping order in Afghanistan so that our troops and other troops can, over time, come home."
Former Afghan foreign minister Dr Abdullah said he had withdrawn from the election's second round because his demands to ensure a fair vote had not been met and a transparent election was not possible.
Mr Brown said the withdrawal was in the interests of national unity.
The electoral run-off was ordered in response to widespread allegations of vote-rigging in the first poll, which was won by Mr Karzai.
Mr Brown said that the president had assured him that "his intention is to build a government that is wider, a government that gets the best people, a government that is free of corruption".
"Afghanistan has got to move forward with a better form of government than we have had over the last few years," he added.