WASHINGTON: The United States should apologise for an air raid that killed 24 Pakistani soldiers if it wants Pakistan to reopen key supply routes into Afghanistan, Foreign Minister Hina Rabbani Khar said in an interview published on Monday.

Angered over the lethal November attack, Islamabad shut the supply routes vital for US and allied troops, forcing the alliance to rely on longer, more expensive northern routes through Russia and Central Asia.

“A representative parliament of 180 million people has spoken on one subject,” Khar told Foreign Policy, referring to new guidelines for US-Pakistan ties approved by Pakistani lawmakers which call for an apology.

A US apology is “something which should have been forthcoming the day this incident happened and what a partnership not only demands, but requires,” she said.

The on-again, off-again relationship between Islamabad and Washington is at a new low, and with US elections looming in November, President Barack Obama is unlikely to say sorry to Pakistan and make himself vulnerable to attacks from his Republican challenger, Mitt Romney.

A Nato summit in Chicago ended two weeks ago without a deal on the Nato supply lines.

Khar however said that despite the political challenges, the United States should live up to its principles of doing “what we consider to be right rather than what is more popular.” She noted that Pakistan also has political obstacles of its own.

“For us in Pakistan... the most popular thing to do right now is to not move on Nato supply routes at all. It is to close them forever,” she said.

“If I were a political advisor to the prime minister, this is what I would advise him to do.

But I'm not advising him to do that... because what is at stake is much more important for Pakistan than just winning an election.”

The roads through Pakistan, now shuttered for over six months, are a crucial logistical link for Nato as it plans a large-scale withdrawal of combat troops and hardware by the end of 2014.

Yet US officials have so far rejected Pakistani proposals to charge steep fees of several thousand dollars for each alliance truck crossing the border.

Khar also criticised Washington's use of unmanned drones to target militants in Pakistan's lawless tribal area, a program Obama has accelerated. “If you are creating 10 more targets for every target you take, are you doing a service or a disservice to your eventual goal of winning the war?” she asked.

Another thorn in the side of the contentious US-Pakistani relationship has been Shakil Afridi, the Pakistani doctor who helped the CIA find late al Qaeda leader Osama bin Laden by running a fake vaccination program, and who was sentenced to 33 years in prison for treason.

“Clearly, my advice at this point is that we don't need to blow this out of proportion at all,” Khar said. “But I would certainly not want this particular issue to cast a shadow over the relationship.”

The interview was conducted in Doha during the May 29-31 US-Islamic World Forum organised by The Brookings Institution.