Such is the state of U.S./Pakistan relations that no one seems fully confident this was accidental. Is there another “alliance” in the world of which that could be said — where one country wipes out two dozen troops from the other and it’s not instantly clear it was a terrible miscalculation instead of a response to some shadowy provocation?

Is it “friendly fire” if the two sides aren’t really friendly?

“It seems quite extraordinary that we’d just nail these posts the way they say we did,” said one senior American official who was in close touch with American and NATO officials in Pakistan and Afghanistan early Saturday. “Whether they were going after people or whether there was some firing from the Afghan side of the border, then the Pakistan side, we just don’t know. It’s real murky right now. Clearly, something went very wrong.”

The American ambassador in Islamabad, Cameron Munter, called an emergency meeting and expressed regret over the Pakistani casualties. And Gen. John R. Allen, the commander of NATO-led forces in Afghanistan, offered condolences to families of the dead and promised an investigation. “This incident has my highest personal attention and my commitment to thoroughly investigate it to determine the facts,” he said in a statement.

The strikes, which Pakistani officials said had involved both helicopters and fighter jets, took place overnight at two military posts in Salala, a village in Pakistan’s Mohmand tribal region near the border with Kunar Province in Afghanistan. At least 40 soldiers were deployed at the posts, which according to Pakistani officials were established to repulse cross-border attacks by Afghan militants and the Taliban. Pakistani military officials said NATO aircraft had penetrated roughly a mile and a half into Pakistan to make the strikes.

If you’re thinking this might be a jihadi operation that Pakistan’s trying to pin on NATO, no dice: A NATO spokesman says it’s “highly likely” that coalition aircraft were responsible. (Why would the Taliban or the Haqqanis want to attack Pakistan at this point anyway?) As punishment for the incident, Pakistani leaders have cut supply lines into Afghanistan and ordered the U.S. to scram from its drone base in southern Pakistan within 15 days. And opposition leaders are already screaming about ending their “support” for the war on terror, so if you’re one of the many people who wonder what things in Afghanistan would look like without Pakistani “help,” good news — we might be about to find out.

I’ll give you three scenarios about what might have happened in the hope/expectation that knowledgeable readers will rule some out in the comments. One: Hot pursuit. NATO was chasing some jihadi outfit, they crossed the border, then we crossed the border after them. It’s happened before and Pakistani troops have ended up dead in the process. But not dozens of Pakistani troops; the sheer volume of casualties plus the fact that NATO surely knows there are checkpoints near the Durand Line makes it hard to understand how this was a case of mistaken identity. Maybe they killed some troops accidentally and then took fire from the others? Or maybe they took fire as soon as they crossed the border? Two: Deliberate targeting. The Times reported six weeks ago about the sustained escalation in mortar fire at American units from across the border in Pakistan. The troops interviewed for the piece made no bones about their belief that the Pakistani military was involved. Ten days after that story was published, the Pentagon made the charge formally. Maybe last night’s attack was NATO’s way of sending a message in the guise of a friendly fire incident. Problem is, doing it this visibly and spectacularly forces the Pakistani leadership to retaliate, as they’ve now done by revoking base rights. Would the White House really risk their drone program just to take out a few Pakistani troops for supporting jihadi mortar fire? Could be that the drone program’s been so successful that they were planning to wind it down anyway, just because there’s almost no one left to target. But Obama’s always preferred stealth operations to spectacles. If he wanted to send a message, he could do it without making Pakistan lose face.

Three: It really was a crazy accident. Gen. Allen met with Pakistani Gen. Kayani on Thursday, just one day before the incident, to discuss greater coordination. Less than a month ago, the White House decided that its (insane) new strategy in Afghanistan was to somehow convince Pakistan to bring the Taliban and the Haqqanis to the bargaining table for talks. If we’re still of the mind that Pakistani cooperation is essential to getting out of the war as quickly and cleanly as possible, mowing down their soldiers en masse seems … counterproductive. So yeah, it probably is an accident — assuming accidents on this scale are even possible. Any Air Force readers willing to weigh in? How likely is it that NATO jets and choppers might not recognize whom they’re engaging on the ground, even when they know there are “allied” checkpoints in the area?