Kabul, Afghanistan (CNN) -- Amid intense international pressure for reform, Afghan President Hamid Karzai vowed to tackle corruption and drug-trafficking in a speech delivered at his inaugural ceremony Thursday.
Karzai was sworn in for a second term following a fraud-marred election that questioned his legitimacy. His inauguration also came a day after a report of grave government graft had surfaced.
"Corruption is a very dangerous enemy of the state," Karzai told about 800 guests assembled in the fortified presidential palace in the Afghan capital, Kabul. Security was tight throughout the city, fraught with the potential for Taliban attacks on inauguration day.
With U.S. Secretary of State Hillary Clinton sitting in the front row, Karzai said he was sorry if he had let his allies down.
"I am sorry if I have not fulfilled anything I have promised," he said. "It's not easy to govern this state."
The Obama administration, considering sending up to 40,000 more U.S. troops to Afghanistan, has expressed concerns about Karzai's viability and has ratcheted up pressure to end corruption in order to combat an intensifying Taliban insurgency.
Clinton reiterated those concerns in a dinner meeting with Karzai on the eve of his inauguration and encouraged him to seize the "clear window of opportunity" before him at a "critical moment" in Afghanistan's history.
Clinton's remarks came after The Washington Post reported that a Chinese firm apparently had secured a contract for a big copper extraction project after a government minister accepted a $30 million bribe.
The Afghan ministry denied the allegation.
"Good governance -- that's what I want," Karzai said. "I want competent ministers who can lead this country."
He said government officials who overstep should be prosecuted. He linked graft to Afghanistan's heroin trade.
"It is our duty to tackle drug traffickers and punish those people who are cultivating poppies," Karzai said.
Before taking the oath of office, Karzai, in his trademark Afghan robe and hat, walked a red carpet outside the hall in a review of security forces while a band played the Afghan national anthem.
After Thursday's pomp and ceremony fade, Karzai will have to get down to the daunting task of quickly steering Afghanistan down a path of reform.
As he began another five years as president, Karzai thanked NATO allies for their sacrifices and assistance in establishing peace and said their training of Afghan forces would be critical. He said he anticipated the country's security to be wholly in the hands of Afghan army and police within five years.
Karzai's inauguration was mired in controversy. He was declared the winner of an August 20 election that was deemed tainted with ballot-stuffing, leaving many Afghans to view their leader as lacking legitimacy.
To that extent, Karzai extended an olive branch to all his "brothers" who ran for president, particularly his chief challenger, Abdullah Abdullah, who was to have been in a runoff with Karzai but withdrew a week before the vote.
Five years ago, Vice President Dick Cheney and three former U.S. presidents attended Karzai's first inauguration. This time, few heads of state were present. One notable exception was Pakistani President Asif Ali Zardari.