The US-Pakistani relationship remains challenging for both despite the reopening of Pakistani land routes to resupply US troops in Afghanistan, US Secretary of State Hillary Clinton said on Sunday.

Clinton last week apologized for a November NATO air strike that killed 24 Pakistani soldiers and Islamabad responded by reopening the overland supply routes that are crucial to the US-led war in Afghanistan.

Speaking after she met Pakistan Foreign Minister Hina Rabbani Khar, Clinton said both were encouraged they had "put the recent difficulties behind us" but she acknowledged the difficulties in the relationship in blunt terms.

"I have said many times that this is a challenging but essential relationship. It remains so. And I have no reason to believe it will not continue to raise hard questions for us both," Clinton said. "But it is something that I think is in the interests of the US as well as in the interests of Pakistan."

Clinton said that the top issue she discussed with Khar was "the necessity of defeating the terror networks that threaten the stability of both Pakistan and Afghanistan as well as interests of the US" and its allies.

Some in Pakistan oppose the decision to reopen the supply lines, and around 2,000 supporters of hardline religious groups rallied in the eastern city of Lahore on Sunday to protest the move. They plan to travel to the capital of Islamabad in a "long march" to demonstrate against the reopening of the routes.

Reuters