A deal between the United States and Pakistan on reopening ground military supply lines into Afghanistan appears almost certain, a U.S. official told Reuters news agency on Tuesday, cautioning however that an agreement had not yet been finalized. The official, speaking on condition of anonymity, said the U.S. military might see some higher costs to receive goods in Afghanistan than it did before Pakistan cut off the supply lines last year. The official did not elaborate, however. Pakistan closed the lines after 24 of its soldiers were killed by a NATO cross-border air attack last November. Pakistan had demanded a formal apology from the United States for the attack before it reopens the supply routes, and had also called for an end to U.S. drone strikes on its tribal areas bordering Afghanistan. Pakistan boycotted an international conference on Afghanistan in Bonn in December in protest against the NATO air strikes. But, Pakistani President Asif Ali Zardari will attend a summit of NATO leaders in Chicago this weekend, the Pakistani embassy in Washington said on Tuesday.