Pakistan cites India's influence in Afghanistan as one of its top concerns. And with Pakistan increasingly crucial to any military or diplomatic progress in the war, it's a concern that Washington has to manage.
Some current and retired Pakistani officials are hinting that as both the war and the peace efforts become more and more difficult, Washington and its Afghan allies might do more to reassure Islamabad that India won't play a major role in a future Afghan settlement.
"That, to my mind, is one of the mysteries: why the Americans have not recognized why the Pakistanis have a legitimate reason to worry about Indian involvement in Afghanistan," says Najmuddin Shaikh, a former Pakistani foreign secretary.
Instead, he says, the US is looking for a "regional solution" that would involve negotiations with not just Pakistan, but nonbordering countries like Russia and India. He calls the inclusion of India "bothersome," and says the only countries for which Afghanistan is "critical" are Pakistan, Iran, and, to a lesser extent, the Central Asian republics.
In the end, Pakistan wants a friendly government in Kabul, and friendship is defined in reference to India.
"They are two sovereign countries, India and Afghanistan, and they have the right to have good relations. But what we are saying is that their relations should not be at the cost of Pakistan-Afghanistan relations, or in any way harm Pakistan's interests," says Abdul Basit, the spokesman for Pakistan's Foreign Ministry.
Pakistan worries about having to defend both its eastern and western borders if India and Afghanistan grow too close. Pakistan has also alleged that India uses its consulates in Afghanistan to conduct espionage, stirring up antigovernment forces in Pakistan's frontier regions.
Verging on paranoia
"I've had Pakistani diplomats tell me, 'You know, there are 15 [Indian] consulates,'" he says. (There are four.) "When you press them on it, they say that, in effect, this is our line," suggesting that they sometimes fabricate in order to have some bargaining leverage.
India did use Afghanistan to aid Balochistan separatists in the 1970s, Dr. Weinbaum says, but no evidence has turned up of meddling in recent years. That said, consulates are "listening posts," he adds.
Ramesh Chopra, a retired head of Indian intelligence, dismisses the idea that consulates are being used for espionage, noting that the border regions are an impenetrable war zone.
Beyond security concerns, Pakistan worries that India has historically supported minority ethnic factions in Afghanistan, creating tensions with the more numerous Pashtuns who live on both sides of the Afghanistan-Pakistan border.
"Pakistan's interest is really that the Pashtuns should have their due share so that they don't then create resentments among the Pashtuns in Pakistan," says Mr. Shaikh. Many Pashtuns are unhappy with the current makeup of the Afghan government and military and that has contributed to the Pashtun-dominated insurgency.
India's stake in Afghanistan
Indian officials bristle at any suggestion that Afghanistan is not a vital interest.
"We are first and foremost in Afghanistan for the same reasons as the rest of the international community: to prevent it from becoming a safe haven for terrorists," says a senior official in India's foreign office.
Under the former Taliban regime, an Indian airliner was hijacked in Kabul and Kashmir jihadis trained in Afghan camps. India also cites historically close relations with Afghanistan, as well as the access to Central Asian trade as important.
But the worst nightmare for India, and the main reason India advocates for a regional agreement, says the official, would be an unraveling of Afghanistan as NATO leaves. He says to guarantee Afghanistan's sovereignty, an effort has to be regional. India argues that other nations have key interests: Iran does not want to see a radical Sunni government return; China worries about similar extremists developing ties with its neighboring Muslim minority.
To help stabilize Afghanistan, India has pledged $1.3 billion in assistance since the Taliban's ouster. It has also implemented some 50 development projects including a road to Iran and transmission wires to Uzbekistan. The country's involvement has come with risk: Militants have launched multiple deadly attacks on the Indian embassy.
"They have an investment there now as far as they are concerned. If things go badly there, you can bet that they will [send] military advisers," says Weinbaum.
India has not contributed militarily to the coalition effort because Afghan President Hamid Karzai has not sought its help, perhaps under US pressure not to antagonize Pakistan.
Quietly the US has talked to the Afghan government about listening to Pakistan's concerns, says Weinbaum.
But publicly the US has mostly celebrated Indian involvement in Afghanistan, not called for less.
Partly this is because India shares American antipathy toward the return of a radical Islamic government, and partly because the US wants to deepen its ties to India.
Asking India to leave "would be contrary to any diplomatic political norms," says Michael Semple, an expert on the current peace process. Instead, a legitimate way to address Pakistan's concerns is by "providing an effective check on any threatening or unhelpful activities."
The Afghan government appears to be taking further steps to ease Pakistan concerns about India. Mr. Karzai last year removed his intelligence chief, a powerful Tajik who was seen as wary of Pakistan and more sympathetic to India. Karzai also sent former Afghan President Burhanuddin Rabbani as head of a High Peace Council to Pakistan earlier this month.
Mr. Rabbani remains a powerful figure among the ethnic minority factions that resisted the Taliban in the 1990s, and though he has received Indian help in the past, he said the right things to put Pakistan at ease.
"What Mr. Rabbani said today was quite meaningful: that no third country would be allowed to damage Afghanistan-Pakistan relations," said Mr. Basit after meetings Jan. 5 between Rabbani and the Foreign Ministry.
"The Afghan government has assured us that they would never allow their soil to be used against Pakistan," added Basit. "But one would also like to acknowledge the fact that there are areas that are not under the Afghan government's control and that can be taken advantage of."