A senior official for the NATO-led forces in Afghanistan on Tuesday strongly denied a report in The New York Times that the United States was considering expanding Special Forces raids into Pakistan.
Tensions between the United States and Pakistan are already strained despite months of strategic dialogue aimed at upgrading the relationship -- and billions of dollars in aid for development and relief from devastating floods.
Analysts said Washington might be using the suggestion to coax Pakistan into tougher action against Taliban militants in areas bordering Afghanistan. But any serious move to expand ground raids would boost tension, perhaps intolerably, and could be considered a "red line" for Pakistani authorities.
"There is absolutely no truth to reporting in the New York Times that U.S. forces are planning to conduct ground operations into Pakistan," Rear Admiral Gregory Smith, Deputy Chief of Staff for Communication for the International Security Assistance Force (ISAF), said in a statement from Kabul.
He said U.S. troops and their NATO-led allies, along with Afghan forces, had "developed a strong working relationship with the Pakistan military to address shared security issues.
"This coordination recognises the sovereignty of Afghanistan and Pakistan to pursue insurgents and terrorists operating in their respective border areas."
Late on Monday, the New York Times reported that senior U.S. military commanders in Afghanistan were seeking to expand Special Operations ground raids into Pakistan.
The proposal, as reported, would escalate military activities inside Pakistan and reflects growing frustration with Islamabad's efforts to root out militants in Pakistani tribal areas, the newspaper said, citing U.S. officials in Washington and Afghanistan.
Pakistani authorities made clear the issue was hypersensitive in what is already a shaky alliance in the U.S.-led war on militancy.
"Pakistani forces are capable of handling the militant threat within our borders and no foreign forces are allowed or required to operate inside our sovereign territory,"
Islamabad's ambassador to the United States, Husain Haqqani said, according to the official Associated Press of Pakistan news agency.
"We work with our allies, especially the U.S., and appreciate their material support but we will not accept foreign troops on our soil -- a position that is well known."
Tensions have already risen sharply.
On Friday, the CIA station chief in Islamabad was recalled because he was named in a criminal case filed in a Pakistani court over deaths in the suspected U.S. drone strike campaign against militants in the tribal areas.
It is likely his name was leaked by Pakistan's powerful spy agency, the Directorate of Inter-Services Intelligence (ISI), possibly in retaliation for a court case filed in a U.S. court implicating the ISI's chief in the November 2008 Mumbai attacks, which killed 166 people.
There has been a marked uptick in drone strikes in areas where they were previously rare. Last week, four drone strikes in two days killed 28 people in Khyber agency.
Most recent drone strikes -- assumed to be directed by the CIA -- have been in North Waziristan, areas long considered a base for al Qaeda and Afghan militants to rest and rearm as they battle allied forces across the border.
The United States, according to the Washington Post, had wanted to expand the strikes to other parts of Pakistan, but was refused by Islamabad.
Pakistan has mounted major campaigns against militants on its Western border, but has long resisted entering North Waziristan, saying it needs to consolidate gains made elsewhere before it can tackle the rugged area.
Analysts say Pakistan is dragging its feet because it wants to maintain the Haqqani network -- based mainly in North Waziristan and one of the most lethal groups in the Afghan insurgency -- as an asset in any future political settlement in Kabul.
"This is a deliberate leak," Ahmed Rashid, a journalist and expert on the Afghan Taliban, told Reuters. "The Americans have been talking about this for the last six months."
Pakistanis, he said, could only react with rage to the possibility of drone strikes on major cities, like Quetta.
But, he added, the United States is more serious this time because if after winter the Taliban can maintain the intensity of their attacks, this could jeopardise the success of President Barack Obama's plan to begin a phased withdrawal in mid-2011.
"So it is absolutely imperative for the Americans to make sure that spring offensive by the Taliban is much reduced," he said. "The way they can do that is obviously to attack Taliban here or maybe pressure Pakistan."
NATO allies, too, are beginning to signal an end to their combat roles in the unpopular nine-year-old war.
The White House said in a review of Afghanistan strategy unveiled last week that while a surge in U.S. troop levels has helped push Taliban fighters out of parts of south Afghanistan, tentative progress cannot be sustained unless Pakistan acts decisively against militants sheltering within its borders.
While the White House said Pakistan had taken steps to crack down on militants, stationing 140,000 troops on its western border, senior officials appear increasingly exasperated. Obama said "progress has not come fast enough" for his liking.
"The relations are very, very tense in my opinion and very bad," Rashid said. "The two governments may be covering it up but I think the relations are very tense."
Kamran Bokhari, Middle East and South Asia director for intelligence firm STRATFOR, was even more direct:
Even the suggestion of U.S. forces in Pakistan "is a red line for Pakistanis," he said. "This is going to create a lot of problems."