The United States will launch a new effort to track down Osama bin Laden who is believed to be hiding in the mountains along the Afghan-Pakistan border, a senior US official said.
Intelligence reports suggest the Al-Qaeda chief "is somewhere inside north Waziristan, sometimes on the Pakistani side of the border, sometimes on the Afghan side of the border," said national security adviser James Jones.
Asked if President Barack Obama's administration planned a fresh attempt to go after Al-Qaeda's leader, Jones said: "I think so."
Bin Laden was a "very important symbol of what Al-Qaeda stands for" and it was crucial to make sure he was on the run or captured, Jones, a retired Marine general, told CNN's "State of the Union" program.
His comment that Bin Laden sometimes crossed to the Afghan side of the mountainous border contrasted with previous accounts from US officials that suggested the Al-Qaeda chief was hiding in Pakistan.
Despite the vow to track down Bin Laden, Defense Secretary Robert Gates said on Sunday that intelligence agencies did not know where the Al-Qaeda leader was and had lacked reliable information on his whereabouts for years.
"We don't know for a fact where Osama bin Laden is. If we did, we'd go get him," Gates, a former CIA director, told ABC News' "This Week."
The Al-Qaeda network leader is seen as the chief mastermind of the attacks of September 11, 2001 on New York and Washington that killed nearly 3,000 people.
US government officials have named Bin Laden and the Al-Qaeda network as the prime suspects in the attacks and offered a 50 million dollar reward, but for more than eight years Bin Laden has avoided capture.
Secretary of State Hillary Clinton said Sunday it was "important" to capture or kill Bin Laden and other Al-Qaeda figures but told NBC that "certainly you can make enormous progress absent that."
A Senate report released last week said Bin Laden was "within the grasp" of American forces in late 2001 in Afghanistan but escaped because then-defense secretary Donald Rumsfeld rejected calls for reinforcements.
In making the case last week for surging 30,000 additional troops into Afghanistan, Obama and his deputies have argued the Taliban are colluding with Bin Laden's network and therefore containing the Afghan insurgents is vital to defeating Al-Qaeda.
The administration has also warned that a victory for the Taliban in Afghanistan could destabilize its nuclear-armed neighbor Pakistan.
Washington has pressed Islamabad to crack down on Taliban and Al-Qaeda strongholds inside its territory and top US officials on Sunday praised Pakistan for launching a military campaign against militants.
On CBS with Gates, Clinton said she saw hope in Pakistan's willingness to take on the Pakistani Taliban.
"You know if you had told us a year ago that the Pakistani army would be going after Pakistani Taliban, I think a lot of people would've said no, that couldn't ever happen, that's not the way it works.
"But they saw the threat to their sovereignty," said Clinton, citing insurgent attacks on government targets in Pakistan.
However, the US special representative to the region, Richard Holbrooke, said Islamabad so far had only targeted insurgents launching attacks inside Pakistan and not the distinct Afghan Taliban leadership using its territory to fight the Kabul government and NATO-led troops across the border.
"It is an unfortunate but unavoidable fact that those military offensives... were directed against the Taliban that were are focused on Pakistan, not the Taliban who are focused on Afghanistan," Holbrooke told CNN.
"That's one of the main issues that we have been talking to our friends in Pakistan about."
Washington has stepped up a bombing campaign against Al-Qaeda leaders in Pakistan using unmanned aircraft, an operation that US officials decline to discuss publicly.
The New York Times reported last week that the White House had granted authority to the Central Intelligence Agency to expand the air strikes in Pakistan to coincide with Obama's Afghan war strategy.
US officials were also talking with Islamabad about using the drones to strike in Baluchistan -- a vast region outside of the tribal areas that borders Afghanistan and Iran -- where Afghan Taliban leaders are reportedly hiding, the Times reported.
Gates said Sunday that US forces would not pursue Taliban leaders in Pakistan and that it was up to the Pakistani military to tackle the militants.