Pakistan's decision to end a seven-month blockade of Nato troop supplies was a rare bright spot in relations with the US, but disagreements over issues like American drone strikes and Islamabad's alleged support for Taliban militants still hamper a relationship vital to stabilizing neighboring Afghanistan.
Even before Pakistan shut down the supply line in November in retaliation for American airstrikes that killed 24 of its troops, the relationship was plagued by anger and mistrust. Islamabad was livid with the unilateral US raid that killed Osama bin Laden in May 2011 and a CIA contractor who shot to death two Pakistanis a few months earlier.
The deadlock over Nato supplies ended Tuesday when the US apologized for the deaths of the Pakistani troops and Islamabad agreed to reopen the route. The accord should ease tensions somewhat, but tackling other problems could prove difficult because the long stalemate that followed the November attack intensified bad feelings in both capitals.
"Given the history of the past 12 to 18 months, there is a huge residue of mistrust and mutual suspicion," said Tariq Fatemi, a former Pakistani ambassador to the US "I would not rule out the possibility of a small incident derailing the normalisation process."
US officials had expected the first trucks carrying Nato supplies to begin crossing into Afghanistan on Wednesday, but bureaucratic delays held that up. Trucks are now scheduled to begin moving across the border Thursday morning, although it will take days to get back to levels prior to the attack, said Pakistani security officials, speaking on condition of anonymity because they were not authorized to talk to the media.
The reopening could save the US hundreds of millions of dollars, since Pakistan's blockade forced Washington to rely more heavily on a longer, costlier route that leads into Afghanistan through Central Asia. Pakistan is also expected to gain financially, since the US intends to free up $1.1 billion in military aid that has been frozen for the past year.
But the deal carries risks for both governments. Pakistan is likely to face domestic backlash, given rampant anti-American sentiment in the country and the government's failure to force the US to stop drone strikes targeting militants and accede to other demands made by parliament.
"It is an insult to our nation," said Maulana Samiul Haq, chairman of the hard-line Difah-e-Pakistan, or Defence of Pakistan Council. "The rulers have put national interest at stake just to please America." Haq pledged his group a collection of Islamist leaders who have been the most vocal opponents to reopening the supply line would launch nation-wide protests against the government's decision and called for Pakistanis to peacefully block Nato trucks from reaching Afghanistan. "It is mandatory for every Muslim to do everything possible to block such supply" to their enemy, he said.
The council is widely believed to be supported by Pakistan's powerful army as a way to put pressure on the US But Haq said Wednesday that the army will be remembered "as a culprit in national history" for supporting reopening the supply line. Islamist groups like Difah-e-Pakistan regularly draw tens of thousands of people to their protests, where they whip up anger against the US that works to constrain Islamabad's level of co-operation with Washington.
The government also faces risk from the Pakistani Taliban, who vowed to attack trucks carrying Nato supplies once they start moving. Many such attacks have occurred in the past, but Nato officials claimed the flow of materiel was not significantly affected.
Pakistan has been fighting a bloody insurgency by domestic Taliban militants but is widely believed to support others who are battling US forces in Afghanistan. The leadership of the Afghan Taliban and the Haqqani network, considered the most dangerous militant group fighting in Afghanistan, is believed to be based in Pakistan and has historical ties to Pakistani intelligence.
Islamabad has denied allegations of support but has refused US demands to target the militants, generating significant levels of anger in Washington. US officials also have pushed Pakistan to use its contacts to urge the Taliban to negotiate a peace deal that would prevent Afghanistan from descending into further chaos as American combat troops withdraw in 2014.
The US held off on saying sorry for the November attack for months, despite Pakistani demands, because President Barack Obama was worried about exposing himself to criticism from Republicans, including presidential challenger Mitt Romney. Romney contends the administration is too quick to apologise in foreign policy matters.
In the end, Secretary of State Hillary Rodham Clinton said the US was "sorry" for the deaths of the Pakistani troops but didn't offer the "unconditional apology" demanded by the country's parliament. Clinton reiterated that mistakes on both sides led to the airstrikes on two army posts on the Afghan border, disputing Pakistan's claim that the US was wholly at fault and carried out the attack deliberately.
Pakistan demanded much higher transit fees during the months of negotiations up to $5,000 per truck but agreed in the end to maintain the $250 price levied before the attack. The US offered extensive road construction projects to sweeten the deal, although officials have not provided specific figures.