Since last week's brazen 20-hour attack on the U.S. Embassy, NATO headquarters and other buildings in Kabul, one issue has topped the agenda in meetings between high-level U.S. and Pakistani officials: How to deal with the Haqqani network, a group closely allied with both the Taliban and al-Qaida that U.S. military commanders have called "most resilient enemy network" fighting against coalition forces in Afghanistan.

The group is named after the ethnic Pashtun father and son who lead it. The elder Jalaluddin Haqqani fought Soviet forces in Afghanistan and later sided with the Taliban during the Afghan civil war. Since NATO forces became involved in Afghanistan following the September 11, 2001 terrorist attacks, the network has reportedly set up bases in North Waziristan, a region of Pakistan along the Afghan border where there is a large Pashtun population.

The issue of Pakistan's relationship with the Haqqanis has been a sensitive topic between Washington and Islamabad for years. Speaking recently on Pakistani state radio, U.S. Ambassador to Pakistan Cameron Munter said Washington is losing patience with Pakistani support for the group.

"We have said in the past that there is evidence linking the Haqqani network to the Pakistani government," he said. "This is something that must stop. We have to make sure that we work together to fight terrorism, to recognize the common enemy, the people who attack Pakistanis, the people who attack Americans, the people who [orchestrated] events like what happened in Kabul."

According to some observers, Pakistani authorities do not view the Haqqanis as a threat because they do not attack Pakistani interests. Analysts also believe Pakistan is using the Haqqanis as a "strategic hedge" in Afghanistan, with an eye to the eventual pullout of U.S.-led coalition forces from the country.

Punjab University Professor Hassan Askari says Islamabad fears that if it bows to U.S. pressure to attack the Haqqanis, it will stir up a virtual hornet's nest that the impoverished and militarily-stretched country can ill afford.

"The worry is that if they go into North Waziristan, they may not quickly succeed, and there will be more suicide attacks and other terrorist activities within Pakistan that will destabilize the country or undermine whatever reputation still exists for the government," he said.

On dangerous ground
Another problem is that the North Waziristan territory from which the Haqqanis operate is mountainous and remote. A very difficult terrain on which to wage military campaigns, the region's local population is fiercely independent and resentful of any control, even by Islamabad. Its border with Afghanistan is long and porous.

Pakistan's former ambassador to Afghanistan, Ayaz Wazir, says the international forces in Afghanistan have the resources to go after Haqqani fighters when they cross over, but when asked about sealing the border itself, he poses a rhetorical question. If the superpowers who came to Afghanistan can’t control the border, how can Pakistan be expected to?

"This porous border which the Soviets could not seal, which the Americans cannot seal, which NATO and American forces together cannot seal," he said. "The might of the world is sitting in the small country called Afghanistan, and if they cannot stop [the group] from entering into the country and creating problems, [how can] a poor country like Pakistan with little resources?"

Still, U.S. pressure to end support for the Haqqani network is mounting. A day after Ambassador Munter made his comments on Pakistani state radio, U.S. Secretary of State Hillary Clinton pressed Pakistan to take action against the network during a meeting with her Pakistani counterpart, Hina Rabbani Khar, on the sidelines of the annual U.N. General Assembly in New York.

Mullen accuses Pakistan of waging 'proxy war'
Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, said that during a meeting with his Pakistani counterpart, General Ashfaq Kayani, he had discussed support given to the Haqqani network by Pakistan's Inter-Services Intelligence agency, or ISI.

"We covered a full range of issues focusing on the danger of the Haqqani network, specifically the need for the ISI to disconnect from Haqqani and from this proxy war that they’re fighting," he said.

Also on Tuesday, Secretary of Defense Leon Panetta said the U.S. would “take whatever steps are necessary" to protect its forces in Afghanistan from attacks by the Haqqani network.

The Washington Post, citing unnamed U.S. and Pakistani officials, reported Wednesday that Obama administration officials have indicated the U.S. will act "unilaterally" if Pakistan does not cut ties with the Haqqani network and "help eliminate its leaders."

According to AFP and The Associated Press, U.S. officials who did not want to be named reported the U.S. has agreed to limit the number of military personnel stationed in Pakistan. Immediately after the U.S. raid on Osama bin Laden's compound in Abbottabad, Pakistan, in May, Pakistani officials called for U.S. to withdraw personnel who were helping train Pakistan's military in counterinsurgency tactics.