ISLAMABAD, Pakistan - The top U.S. commander in Afghanistan held talks with Pakistan's army chief Saturday aimed at improving border coordination, almost six months after American air strikes accidentally killed 24 Pakistani soldiers along the frontier.

Islamabad retaliated for the deaths in November by closing its border crossings to supplies meant for NATO troops in Afghanistan. The border remains closed despite U.S. pressure to reopen the route, which has long been one of the main ways to get goods and equipment to coalition forces.

Pakistan's parliament has demanded that Washington apologize for last year's attack and stop drone strikes targeting militants in the country's tribal region along the Afghan border. Although Pakistani lawmakers have not explicitly linked these issues to reopening the supply route, the matters have complicated the discussions.

The United States has expressed its condolences over the deaths of the Pakistani soldiers at two Afghan border posts, but has stopped short of issuing a full apology, likely because of domestic political considerations. The Obama administration may fear criticism from members of Congress and Republican presidential contender Mitt Romney, given anger toward Pakistan for allegedly coddling militants attacking U.S. troops in Afghanistan.

U.S. officials have made clear in private they have no intention of stopping covert CIA drone strikes in Pakistan, and several attacks have occurred since the parliament demanded they stop.

The issue is complicated by the fact that Pakistan is widely believed to have supported some of the strikes, although that cooperation has come under strain as the relationship between Washington and Islamabad has deteriorated.

Despite the disagreements between the two countries, Saturday's talks between U.S. Gen. John Allen and Pakistani army chief Gen. Ashfaq Parvez Kayani indicated some level of progress in the relationship. The meeting, which the Pakistani army announced in a written statement, followed several other discussions between senior U.S. and Pakistani officials in recent weeks.

There is incentive on both sides to resolve the impasse over the NATO supply route. The United States has had to spend considerably more money over the last few months shipping supplies to Afghanistan through the more expensive northern route that runs through Central Asia. The route through Pakistan will become even more important as the United States begins to pull out equipment as it withdraws most of its combat troops from Afghanistan.

Islamabad is eager to free up more than $1 billion in U.S. military aid that has been frozen for the last year and that would likely be released only once the supply route is reopened. Another potential carrot could be an invitation to the NATO summit in Chicago May 20-21, which will largely focus on the Afghan war.