WASHINGTON—The U.S. is pulling its negotiating team from Pakistan without a deal to reopen critical U.S. and allied supply lines for forces in neighboring Afghanistan, officials said Monday, the latest wrinkle in long and contentious talks.

Despite the apparent fracture, however, U.S. and Pakistani officials said many of the details of a proposed deal to reopen the border crossing have been tentatively agreed. U.S. officials said they were awaiting a decision by Pakistani leaders and were ready to send back their negotiators.

On one negotiating point, money, the U.S. signaled it was willing to raise the per container cost to about $500 from about $240, to upgrade Pakistani roads and to release more than $1 billion in military aid payments withheld since last year, officials briefed on the negotiations say.

But Pakistani officials continue to demand an apology from the U.S. for a Nov. 26 border incident in which U.S. aircraft killed 24 members of the Pakistani military, prompting Islamabad to close supply routes. The U.S. has refused to apologize, saying mistakes were made by forces on both sides.

U.S. and Pakistani officials said last week that a deal appeared to be within reach to reopen the crossings.

But tensions have flared over stepped-up U.S. drones strikes in Pakistan´s tribal areas and over Defense Secretary Leon Panetta´s sharp criticism of Islamabad for refusing to crack down on the Haqqani militant network, which has been behind a wave of attacks on U.S. and Afghan forces in Afghanistan.

In fact, some American officials have suggested Pakistan owes the U.S. an apology for harboring militants who attack allied troops in Afghanistan.

White House press secretary Jay Carney said Monday that while the U.S. relationship with Pakistan remains complicated, he believed a deal remained close. "We believe that all can be resolved, and we remain ready to conclude this agreement as soon as Pakistan is ready," Mr. Carney said.

Pakistan´s ambassador to the U.S., Sherry Rehman, said Islamabad decided to close the crossings in response to the 24 deaths, "absent an expression of remorse."

"We are at a critical stage of discussion and we are still optimistic that we can reach a mutually satisfactory resolution to these issues," she said.

U.S. defense officials want to reopen Pakistan´s border with Afghanistan because moving supplies through Pakistan is significantly cheaper than other distribution routes and because some equipment is too large to be flown out of the landlocked country. U.S. officials also believe a deal is a critical first step toward improving relations with Pakistan, which it needs to increase pressure on militants that take refuge in the border area with Afghanistan.

Some members of the American negotiating team left over the weekend, said George Little, the Pentagon´s press secretary. Others will leave soon.

But Mr. Little said there was "an agreement in concept" and that military representatives in Islamabad will continue to negotiate with Pakistani officials.

An American defense official, Peter Lavoy, arrived in Pakistan last week to try to help finish a deal. Mr. Lavoy was refused a meeting with Pakistan´s military chief, Gen. Ashfaq Parvez Kayani.

However, it would have been considered unusual for Mr. Lavoy, a principal deputy assistant secretary of defense for Asian and Pacific security affairs, to secure a meeting with Gen. Kayani, the most senior member of the Pakistani military.

As the talks have gone on, U.S. officials have emphasized they have alternatives to the Pakistani route, and aren´t as dependent on it as they once were.

On Monday Lt. Gen. Mike Scaparrotti, the commander of day-to-day military operations in Afghanistan, said the closing of the Pakistan border hasn´t affected his forces.

"We´ve continued to build the supplies that we have in Afghanistan," Gen. Scaparrotti said. "We´ve continued to do our job. It´s not really affected us. And I don´t expect it to be a problem here in the future."

But Gen. Scaparotti said that he hoped relations with Pakistan would improve, and that the Pakistanis would take action against the Haqqani network.

"I have talked to my Pakistan counterparts about is the need for them to take on the Haqqani network in that sanctuary, because it is a threat to us, it´s one of the most lethal threats, but it´s certainly a threat to them as well," he said.

Islamabad initially demanded as much as a 30-fold increase in fees per military container for crossing the border into Afghanistan, an increase rejected by the U.S. as unacceptably high.

On Monday, Mr. Little reiterated that the U.S. believed it was critical for Pakistan to do more, but tried to strike a hopeful tone about relations with Islamabad.

"This is something we need to work through with the Pakistanis," Mr. Little said. "We believe we can establish a relationship that produces the kind of action that is required." (Copyright © Dow Jones & Company, Inc.) 06/12/12)