The U.S. military is pulling negotiators out of Pakistan after they failed to reach an agreement with Pakistani officials on reopening NATO supply lines into Afghanistan.

Pentagon spokesman George Little told reporters Monday that the negotiating team had been in Pakistan for about six weeks. He said that in the absence of a deal to reopen the routes, the negotiators are being called home.

“Some of the team has left Pakistan. We expect the other members of the team to leave soon unless circumstances change. That is not to be taken as a sign of our unwillingness to continue the dialogue with the Pakistanis on this issue.”

The decision came after the Pakistani government refused to let a senior U.S. defense official, Peter Lavoy, meet with Pakistan Army Chief of Staff General Ashfaq Kayani.

Islamabad closed NATO supply lines into Afghanistan last November after U.S. airstrikes mistakenly killed 24 Pakistani troops near the Afghan border. Pakistani officials demanded an unconditional apology for the cross-border attack, but Washington refused and only offered condolences.

The attack prompted Pakistan's parliament to review its future engagement with the United States, with lawmakers calling for an end to U.S. drone strikes on Pakistani soil.

Washington withdrew as much as $3 billion of promised military aid. U.S. officials also expressed frustration about what it said was Pakistan's failure to do more to stop members of the militant Haqqani network from using Pakistan to launch attacks on NATO forces in Afghanistan.

With the routes through Pakistan blocked, U.S. military officials had to find alternative supply lines through other countries. They said the closure has not hampered operations.

A commander with the International Security Assistance Force, U.S. Lieutenant General Curtis Scaparrotti, spoke to reporters at the Pentagon via video link from Afghanistan.

“We have continued to do our job. It has not really affected us and I do not expect it to be a problem here in the future. We have several other means and they are providing sufficient re-supply for our forces.”

U.S. defense officials said the supply route issue remains open and said they hope to send negotiators back to Pakistan as soon as there is an indication of progress.