In a tepid statement, the Council "acknowledged" rather than welcomed the conclusion of the tumultuous electoral process where Karzai was declared the winner after challenger Abdullah Abdullah withdrew from a runoff race saying it could not be free or fair.

Abdullah on Wednesday called Karzai's victory illegal and his government a failure, saying the president's tainted administration would not be able to check corruption or fend off the Taliban.

Ban acknowledged there were problems with the elections, following a closed-door meeting briefing the Security Council on his recent trip to Afghanistan. The U.N.'s most powerful body said nonetheless that it looked forward to working with Karzai. It urged him to improve security, promote good governance and fight corruption and the narcotics trade.

The statement and Ban's comments come on a day when British Prime Minister Gordon Brown toughened his tone toward the Afghan leadership. "I am not prepared to put the lives of British men and women in harm's way for a government that does not stand up against corruption," he said Friday in London.

President Barack Obama had earlier warned Karzai that he must fight corruption, just as the U.S. must decides whether to raise troop levels or redefine the goals of the NATO-led mission.