But the idea, which U.S. officials say comes up every couple of months, has been consistently rejected because the White House believes the chance of successfully rooting out the deadly Haqqani network would not be worth the intense diplomatic blowback from Pakistan that inevitably would ensue.
Members of the Haqqani tribe have been targeted by pilotless U.S. drone aircraft, but sending American and Afghan troops into Pakistan would be a serious escalation of the hunt for terrorists and potentially the final straw for Pakistan, already angered over what it sees as U.S. violations of its sovereignty.
The al-Qaida-allied Haqqani tribe runs a mafia-like smuggling operation and occasionally turns to terrorism with the aim of controlling its territory in eastern Afghanistan. The Haqqanis use Pakistani towns to plan, train and arm themselves with guns and explosives, cross into Afghanistan to attack NATO and Afghan forces, then retreat back across the border to safety.
The latest round of debate over whether to launch clandestine special operations raids into Pakistan against the Haqqanis came after the June 1 car bombing of Forward Operating Base Salerno in eastern Afghanistan that injured up to 100 U.S. and Afghan soldiers, according to three current and two former U.S. officials who were briefed on the discussions. The officials spoke on condition of anonymity to describe the still-evolving debates.
The officials told the AP that recent discussions of clandestine ground attacks have included Gen. John Allen, the senior U.S. commander in Afghanistan, as well as top CIA and special operations officials.
Allen's spokesman, Navy Cmdr. Brook DeWalt, said Allen "has not and does not intend to push for a cross-border operation."
The White House and the CIA declined to comment for this story.
Pentagon spokesman George Little said the U.S. was still focused on U.S.-Pakistan cooperation.
"The key is to work together with Pakistan to find ways of fighting terrorists who threaten both the United States and Pakistan, including along the Afghan-Pakistan border, where extremists continue to plot attacks against coalition forces and innocent civilians," he said.
The U.S. relationship with Pakistan is arguably at its lowest point over the continuation of drone strikes to hit terror targets in Pakistan, the successful Navy SEAL raid in Pakistan to kill Osama bin Laden that was carried out without a heads-up to the country's leaders and the U.S. refusal to apologize for a border skirmish in which the U.S. mistakenly killed 24 Pakistani troops. On Thursday, the State Department's inspector general accused the Pakistani government of harassing U.S. Embassy personnel.
Pakistan has done little in response to repeated U.S. requests for a crackdown on the Haqqanis, and Defense Secretary Leon Panetta surprisingly voiced that frustration in a visit to Kabul this month.
He said the U.S. was "reaching the limits" of its patience with Pakistan's failure to tackle the tribe's safe havens. He added that the U.S. was "extraordinarily dissatisfied with the effect that Pakistan has had on the Haqqanis." He also made fun of Pakistan's ignorance over the bin Laden raid at a speech in India, Pakistan's archrival.
Pakistan's army has attacked militant strongholds across the tribal areas, except for North Waziristan, where the Haqqanis hold sway and shelter both al-Qaida and Taliban militants. Pakistani officials say that they intend to hit North Waziristan but that their army is too overstretched to move as fast as the U.S. demands.
Pakistani officials have conceded privately, however, that they have been reluctant to take on the powerful tribe for fear of retaliatory strikes.
To make up for Pakistan's inaction, the CIA's covert drone program has targeted Haqqani leaders, safe houses, bomb factories and training camps inside Pakistan, and special operations raids have hit Haqqani targets on the Afghan side of the border, but that has failed to stop Haqqani attacks on U.S. and Afghan troops and civilian targets.
The officials say Allen expressed frustration that militants would attack and then flee across the border in Pakistan, immediately taking shelter in urban areas where attacking them by missile fire could kill civilians.
The officials say options that have been prepared for President Barack Obama's review included raids that could be carried out by U.S. special operations forces together with Afghan commandos, ranging from air assaults that drop raiders deep inside the tribal areas to hit top leaders to shorter dashes only a few miles into Pakistan territory.
The shorter raids would not necessarily be covert, as they could be carried out following the U.S. military principle known as "hot pursuit" that military officials say entitles their forces to pursue a target that attacks them in Afghanistan up to 10 kilometers (6.2 miles) inside a neighboring country's territory.
The U.S. has staged two major raids and other minor forays into Pakistan's tribal territory before during the George W. Bush administration; the most contentious was in September 2008 when Navy SEALs raided an al-Qaida compound. The operators killed their target, but the ensuing firefight triggered a diplomatic storm with Pakistan.
Rather than fly in, which U.S. military planners at the time feared would alert the Pakistanis, the SEALs marched across the mountainous border, arriving later than planned because of the harsh terrain and just as the fighters were waking for morning prayers, according to one current and one former U.S. official. They spoke on condition of anonymity to discuss the clandestine operation.
Everyone inside the targeted compound opened fire on the SEALs, including the women, one of whom lightly wounded one of the American operators. The firefight also woke the entire village, which joined in the battle, so the SEALs had to call for strafing runs by Black Hawk helicopters to beat them back.
At least one woman and one child were among the many dead.