Kabul  - Afghan President Hamid Karzai promised Tuesday to assemble a government of "national unity," a day after the presidential runoff was cancelled and he declared the winner.

His new cabinet would include representatives from all of Afghanistan's ethnic groups and political camps, Karzai said in Kabul.

The president left open whether the new administration would include the man he was to have faced in Saturday's runoff, Abdullah Abdullah.

Karzai's onetime foreign minister came in second after Karzai in the August 20 election but on Sunday withdrew from the runoff, alleging that it, like the first round of voting, would not be fair.

The August election was marred by massive fraud, mostly in favour of Karzai. A UN-backed investigation discounted about 1 million ballots, or one-third of Karzai's votes, forcing him into the runoff.

But with Abdullah's withdrawal, the Afghan Independent Election Commission on Monday called off the runoff and declared Karzai the winner. However, the method of Karzai's re-election to a new five-year term cast doubts over the legitimacy of his new government.

He said Tuesday that he would make fighting corruption, for which is government has long been criticized, a priority.

A day earlier, US President Barack Obama urged Karzai to begin a "new chapter" for his country by initiating reforms and cracking down on graft.

Obama telephoned Karzai after he was declared the election winner to offer congratulations but also to urge him to get serious about improving the government, fighting corruption and speeding up the training of Afghan security forces.

"The proof is not going to be in words; it's going to be in deeds," Obama said at a meeting with Swedish Prime Minister Fredrik Reinfeldt. (dpa)