White House press secretary Jay Carney put the onus on Pakistan to resume serious talks.
"We saw it as the right move to withdraw" the U.S. negotiating team, he said, adding that it had largely completed its work. "We are ready to send officials back to Islamabad when the Pakistani government is ready to conclude the agreement."
Carney said several issues remain unresolved, but gave no details.
The disagreement over the supply routes is one of numerous tensions in the U.S.-Pakistani relationship. In recent days, the Americans have emphasized their frustration at Pakistan's refusal to do more to stop Pakistani-based insurgent groups from crossing into Afghanistan to fight U.S., Afghan, and allied troops.
Officials in Washington and Islamabad would not detail what led to the break in the supply-route talks, but two senior U.S. officials familiar with the negotiations said the Pakistanis were holding out for an apology for the deaths in November of 24 Pakistani soldiers in a U.S. air strike, which was what triggered Pakistan to close the border. The officials spoke on condition of anonymity because of the sensitivity of the negotiations.
The United States has insisted it will do no more than express regret for the deaths and will not apologize.
The border crossings had been an important means of getting U.S. war materiel into Afghanistan. Since then, NATO and the United States have been using a circuitous, more costly northern route to bring supplies to the war front.
Although the U.S. administration would like to have access to the Pakistani ground supply routes, officials have said they can continue the war and arrange the scheduled withdrawal of U.S. and allied troops and equipment without the routes.
