It doesn't appear to be a permanent break, but the fact that US negotiators are going home without securing a supply line from Pakistan into Afghanistan only shows the depth of the fracture in relations between the two countries.

Wall Street Journal:

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.

Don't worry. We won't blame Pakistan for harboring terrorists who kill American troops in Afghanistan anytime soon. We don't want to offend the Pakistani military, considering all the marvelous help they give us in attacking terrorists inside Pakistan.

We've already expanded other supply routes into Afghanistan so to see Pakistan trying to hold us up by doubling the per container rate and demanding a humiliating apology because their soldiers fired on our aircraft is a little much. I suspect we'll give in though because it's still cheaper to ship through Pakistan than anywhere else.