Ground-to-ground rockets fired within Pakistan have landed on or near American military outposts in one Afghan border province at least 55 times since May, according to interviews with multiple American officers and data released in the past week. Last year, during the same period, there were two such attacks.

May is also when members of a Navy Seals team killed Osama bin Laden in the house where he lived near a Pakistani military academy, plunging American-Pakistani relations to a new low. Since then, the escalation in cross-border barrages has fueled frustration among officers and anger among soldiers at front-line positions who suspect, but cannot prove, a Pakistani government role…

“I don’t have the smoking gun,” said Col. Edward T. Bohnemann, who commands the 172nd Infantry Brigade, which has hundreds of American soldiers in outposts near the border. “Do I have my thoughts, just because it happens so often? Yes, I have my thoughts. But there isn’t a smoking gun.”…

“The level of command and control, and the level of sophistication of the IDF, is showing that there is some type of expertise being employed,” said one American officer, using the acronym for indirect fire, the term the military uses for mortar, artillery and rocket attacks. The officer spoke on the condition of anonymity because of the diplomatic tensions.