President Barack Obama said Monday that the United States is looking forward to a closer cooperation with Afghan government led by President Hamid Karzai, but urging Kabul to improve governance and fight against corruption.

Afghan President Hamid Karzai waves as he waits to meet U.N. Secretary-General Ban Ki-moon in Kabul November 2, 2009. Ban made a surprise visit to Afghanistan on Monday as pressure grew to abandon plans for a risky run-off vote after the withdrawal of Karzai's only rival. [Xinhua/Reuters Photo]

Obama, after meeting with Sweden's Prime Minister Fredrik Reinfeldt in the White House, told reporters that he has phone called Karzai for congratulating the Afghan leader for winning the presidential election.

According to Obama, he also asked Karzai to make "a much more serious effort to eradicate corruption," and to realize that it is the time for the United States and Afghanistan to "write a new chapter based on improved governance."

Reports here said the United States has been dissatisfied with Karzai, who ruled Afghanistan since the Taliban was overturned in 2001, for his failure to secure the country from Taliban attacks, governmental corruption, drug-trafficking and his close ties with warlords.

After top challenger Abdullah Abdullah withdrew from the presidential run-off election set on November 7, the Afghan Independent Election Commission on Monday announced the run-off election has been canceled with Karzai winning the election.

Accused Karzai of failing to meet his demands for a fair and transparent vote, Abdullah said Sunday that he decided to quit the election.

The first-round election was held on August 20, with preliminary results by Afghan election authority showing Karzai won 54.6 percent. However, an UN-backed investigation panel accused the election of widespread fraud and pushed Karzai's total to below the 50 percent, which is needed to avoid a runoff.

"Although the process was messy, I'm pleased to say that the final outcome was determined in accordance with Afghan law," said Obama, adding that the United States would continue to partner with Karzai and his government in "achieving prosperity and security in Afghanistan."

"We are looking forward to consulting closely with his government in the weeks and months to come to assure that the Afghan people are actually seeing progress on the ground," said the president.

Earlier on Monday, Obama's spokesman Robert Gibbs said Washington recognized Karzai as the legitimate leader of Afghanistan and would continue conversation with Kabul over "governance, civil society, and corruption" in order to ensure that "we have a credible partner in our efforts to help secure the country."

The Obama administration, who vowed to disrupt, dismantle and defeat al-Qaeda and its extremist allies, has been reviewing an overall strategy of the war in Afghanistan, and considering whether to send additional troops to the war-torn country.

General Stanley McChrystal, top U.S. commander in Afghanistan, warned that the United States would lose the war against al-Qaeda and Taliban without rapidly sending up to 40,000 additional troops to Afghanistan.

By the end of this year, according to previous deployment plans, there will be a total of 68,000 U.S. troops in Afghanistan.