The U.N. Security Council joined calls Friday on Afghan President Hamid Karzai to fight corruption, with Secretary-General Ban Ki-moon calling the country's political situation "delicate" following deeply flawed elections.

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.

"It is obvious that the political situation remains delicate," Ban said. "Clearly, the recent elections were seriously flawed."

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.

Ban said that during his meeting with Karzai: "I strongly stressed the need for good governance in the country and to take all determined measures against corruption."

Ban noted that Karzai said in his acceptance speech that "he would do his best efforts to eradicate corruption."

"The international community will closely work with him and will continue to urge him to keep his commitment," the secretary-general said.

Ban said he also discussed improving security for U.N. staff following the Oct. 28 attack on a private guesthouse where dozens of U.N. staffers lived, killing five U.N. workers and three Afghans. The Taliban claimed responsibility for the assault, saying they intentionally targeted U.N. employees working on the presidential election.

The United Nations announced Thursday it is sending about 600 foreign staff either out of the country or into secure compounds because of the attack.

Ban told reporters Friday that about 200 will relocate to other U.N. offices in the region in a phased way.

The secretary-general said the U.N. is also reassessing the 93 guest houses in the country to determine which have good security, which need security to be improved, and which will be vacated.

He said a new residential compound for U.N. staff will be bought or built within 12 months.