A quiet but urgent manhunt is under way - stretching from the arid deserts on the borders of Afghanistan near Pakistan's southwestern Balochistan province, to the forbidding mountains in the country's north - for the world's most wanted man, Osama bin Laden.
Forces in Pakistan and Afghanistan are following clues provided by Khalid Sheik Mohammed, the alleged mastermind of the Sept. 11 attacks, who was arrested March 1. At least they say they are following the clues.
Some analysts suggest that regardless of the quality of the information coming from Mr. Mohammed, US and Pakistani officials are hoping Mr. bin Laden will fear his location has been compromised and make a dash into the open.
"[Mohammed's] arrest has given a new life to the hunt for Osama," says Pakistan's Interior Minister Faisal Saleh Hayat. "He has given vital and invaluable information that can help us break the Al Qaeda network domestically and internationally," the minister boasted.
A Pakistani intelligence official says Mohammed is currently being interrogated by US officials at Bagram airbase, north of Kabul, Afghanistan. Mohammed was flown out of Pakistan after three days of joint Pakistan-US interrogations, according to Pakistani officials.
They say handwritten letters by bin Laden in Arabic were recovered from Mohammed suggesting that bin Laden is alive. "He said he had met bin Laden a few months ago near a hilly terrain but did not know the exact area," a senior security official says.
"I don't think he talked lies," says Mr. Hayat. "Initially he gave contradictory statements about Osama but then surrendered before the interrogators. Even if he is misleading, we have to follow the leads,"
Mohammed had fled Balochistan after the arrest of Mohammed Abdur Rehman, an Egyptian Al Qaeda member, in mid-February, and it is generally believed he met bin Laden shortly before that.
On Saturday, US officials at Bagram said they have arrested seven suspected Al Qaeda men in Helmand, Afghanistan. Pakistan and US officials denied reports that two of bin Laden's sons had been captured.
But two Pakistani intelligence officials based in southwest Balochistan province insist that US forces captured two of bin Laden's sons on Thursday in Ribat. "They were injured and are being held in the hospital there," says one. He adds that five others were killed in the operation. He says that one of the sons was named Saad bin Laden.
Bin Laden does have a son named Saad, believed to be 23 years old, who is also on the American most-wanted list and has been called a rising star in the terror network. Senior Pakistani and US officials have denied that the reports are true. "These are simply rumors," says Shoaib Suddle, the inspector-general of police in Balochistan.
Bagram spokesman Col. Roger King also said Saturday that no US-led coalition force had operated in Ribat during the previous 72 hours. That denial, say some observers, left open the door to a CIA paramilitary operation in the region.
With reignited hopes of catching bin Laden, American helicopters are dropping leaflets in the border towns of Afghanistan in the south, offering a $25 million reward for help in the arrest of bin Laden and the Taliban's spiritual leader, Mullah Omar.
On the Pakistani side, troops guided by US intelligence experts are searching in Balochistan's western areas bordering with Iran and along the northwestern borders near Afghanistan.
While publicly denying it, a Pakistani military official says that Pakistan's paramilitary troops have been put on alert on the checkposts along the porous Pakistan-Afghanistan border in the remote areas of Chaghi district, in the inaccessible hills of Helmand provinces, and in Dalbandin and Sandak, which open into the Rabat desert of Afghanistan's Nimroz province.
This area converges into a triangle between Pakistan, Afghanistan, and Iran, infamous as the route of Afghan drug smugglers.
The search for bin Laden and his lieutenants is also continuing in the northwest border with Afghanistan in the mountainous Chitral region, north of the tribal belt, facing Afghanistan's northeastern Nooristan and Kunar provinces. There are reports of US troop movements on the Afghan side of the border.
"We do not know the exact whereabouts of Osama, but he is not in Pakistan," Hayat insists. "But with the arrest of Khalid Sheik Mohammed we will be able to end the active or sleeper cells in Pakistan."
Pakistani officials claim that they have a "great" relationship with US intelligence agencies, but observers say Americans have minimum trust for Pakistan's intelligence agencies.
"Mainly the arrest of Al Qaeda leaders has been possible with the interception of phone calls and with the help of the sophisticated communication system of Americans," says a Pakistani official on the condition of anonymity. "At times, Americans inform Pakistani officials minutes before the raid on Al Qaeda suspects fearing the information might be leaked."
The former chief of Pakistan's Inter Services Intelligence Agency (ISI), Hameed Gul, who headed the agency during the Afghan War in the 80s, says: "Security agencies are a part of the ethos of the country and now the national ethos is hatred against America. What America is doing in Pakistan is unlawful," he says.
"Islamic extremists have supported strategic and national interest of Pakistan. They did not do anything wrong," he says, reflecting the mindset of a section of the country's security agencies.
In any case, catching bin Laden won't be easy. Investigators believe that he does not use telecommunications and now relies on sending written messages through a chain of messengers.
"It seems that they do not have exact clues about bin Laden even now, but they are searching with a strong hope,"says Pakistani analyst Salim Shahid. "It is to be seen whether the Americans rely only on the help of greedy Afghan commanders lured by massive dollar rewards as in Tora Bora, or are acting on solid information gleaned after Khalid's arrest."
• Gretchen Peters contributed from Quetta, Pakistan.