A drone strike a week ago killed Anwar al-Awlaki, a propagandist viewed as "chief of operations" for al-Qaeda in Yemen.
President Barack Obama, marking the 10th anniversary of the US military campaign in Afghanistan, said on Thursday that al-Qaeda was on the ropes but "enormous challenges" remain to rebuild the country.
"In delivering justice to Osama bin Laden and many other al-Qaeda leaders, we are closer than ever to defeating al-Qaeda and its murderous network," Obama said in a statement.
A US drone strike a week ago killed Anwar al-Awlaki, a militant American-born propagandist viewed as "chief of operations" for al-Qaeda in Yemen. That was the latest killing of top al-Qaeda officials since the shooting of bin Laden at his hide-out in Pakistan in May.
The United States and its allies launched the Afghan war on Oct. 7, 2001, to topple the Taliban government sheltering the al-Qaeda leadership responsible for the Sept. 11 attacks on the United States that killed nearly 3,000 people.
Covert US strikes against militants have grown significantly under Obama, particularly in the lawless region along the Afghanistan-Pakistan border, marking a US policy success compared with mixed results from the wider war.
Obama acknowledged "enormous challenges that remain in Afghanistan" -- alluding to violence in which nearly 1,800 US personnel have died, assassinations of government figures and deep corruption -- but still he claimed progress.
"We've pushed the Taliban out of its key strongholds, Afghan security forces are growing stronger, and the Afghan people have a new chance to forge their own future," he said.
Washington's war strategy has been complicated by Pakistan, which Obama said during a White House news conference on Thursday had resisted cutting ties with "unsavory characters" as it hedged its bets on Afghanistan's future.
White House press secretary Jay Carney said the US strategy had suffered setbacks and successes in Afghanistan but the president's prime goal to "disrupt, dismantle and ultimately defeat al-Qaeda" was on track.
NATO, which now heads the Afghan mission, says the overall security situation in Afghanistan has improved and Taliban attacks have declined. But dangers remain.
Afghan President Hamid Karzai, himself the target of a recent assassination plot, acknowledged in a BBC interview on Friday his government and its foreign backers had failed to provide security to ordinary Afghans.
Violence has mounted, with the US embassy in Kabul attacked by militants last month and former Afghan President Burhanuddin Rabbani, who was leading negotiations with militants to end the war, was killed at home on Sept. 20.
The United States will withdraw 10,000 troops from Afghanistan by year-end and 23,000 more by next summer, as the United States and its NATO allies work toward handing over security to full Afghan control by the end of 2014.
"After a difficult decade, we are responsibly ending today's wars from a position of strength," Obama said.
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