[新闻背景]Despite the participation of Pakistani President Asif Ali Zardari at the NATO summit in Chicago, neither the U.S. nor Pakistan announced steps to improve relations or to reopen key NATO supply routes to to Afghanistan. Pakistan closed the lines in November following a U.S. airstrike that killed two 24 Pakistani soldiers.

Pakistani President Asif Ali Zardari  and U.S. Secretary of State Hillary Clinton appeared cordial at their brief meeting at the NATO summit in Chicago. But relations between the two countries remain at an impasse.

Pakistan’s presidential spokesman, Farhatullah Babar, said President Zardari came to Chicago to express his country’s support for NATO’s efforts in the region.

“The president also emphasized that Pakistan wants peace and stability in Afghanistan," he stated. "The president dispelled the misperceptions about the alleged links with the groups of militants of Pakistan.”

But there was no breakthrough to reopen the NATO supply route to Afghanistan that Pakistan shut down last November. NATO has since established a more expensive alternative northern supply route through other Central Asian countries.

Anti-American sentiment in Pakistan has intensified since the U.S. led airstrike in November and the U.S. military raid that killed Osama bin Laden last May. Pakistan’s parliament has demanded an unconditional apology for the airstrike and an end to drone attacks in the border region with Afghanistan, even though media reports say Pakistani intelligence services are secretly aiding the U.S. to identify militant targets.

The U.S. has expressed regret for the airstrike in November, but defends the drone attacks as essential to fighting al-Qaida and other insurgent groups.

President Obama also met briefly with the President Zardari.

"We need to work through some of the tensions that have inevitably arisen after 10 years of our military presence in that region," he said.

Former U.S. ambassador to NATO Kurt Volker says the underlying issue is a lack of trust both about Pakistan’s commitment to fight Taliban extremists and the U.S. promise to maintain a reduced military presence in Afghanistan after most combat troops leave in 2014.

“Both in the side of Pakistan where they say they want support of a stable Afghanistan but in reality they are working to undermine that, and on the American side where we say we have a long term commitment to Afghanistan but we are massively working on the troops withdraws and talking about ending this war,” said Volker.

U.S. and Pakistani officials say they are close to working out their differences, but the lack of progress at the NATO summit seems to indicate the two sides remain far apart.