In an unmistakable snub, President Barack Obama left Pakistan off a list of nations he thanked Monday for help getting war supplies into Afghanistan.

The omission speaks to the prolonged slump in U.S. relations with Pakistan that clouded a NATO summit where nations were eyeing the exits in Afghanistan.

Tensions that Obama readily acknowledged raise questions about whether Pakistan will help or hurt the goal of a stable Afghanistan. Continued mistrust between the United States and Pakistan also threaten cooperation to eliminate al-Qaida sanctuaries and could undermine U.S. confidence in the security of Pakistan's growing nuclear arsenal.

"We need to work through some of the tensions that have inevitably arisen after 10 years of our military presence in that region," Obama said later. "I don't want to paper over real challenges there."

Pakistan is not a NATO member but was invited to the summit Sunday and Monday because of its influence in next-door Afghanistan and its role until last year as the major supply route to landlocked NATO forces there.