American and Afghan soldiers near the border with Pakistan have faced a sharply increased volume of rocket fire from Pakistani territory in the past six months, putting them at greater risk even as worries over the disintegrating relationship between the United States and Pakistan constrain how they can strike back. 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, the New York Times in a report said on Monday. Since May, 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. The governments relations with the United States frayed further after senior American officials publicly accused Pakistan of harboring and helping guerrillas and terrorists. Pakistani officials have repeatedly denied aiding fighters for the Taliban and the Haqqani militant network, who operate on both sides of the border. They insist they try to prevent cross-border incursions or violence. In this climate, American officers were in a difficult position when describing the attacks. Many, especially those who might be identified, painstakingly tried not to blame Pakistan directly. I dont 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. But other officers viscerally rejected Pakistans official position, and said elements of the Pakistani military or intelligence service were most likely involved. 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. The precise reasons for the increase in rocket fire are unclear. Whether the surge in attacks indicates Pakistani military retaliation, an emboldened insurgency, some degree of both or some other factors cannot be determined from the data alone. The attacks covered by the militarys data included those on three American-Afghan outposts Forward Operating Base Tillman, Combat Outpost Boris and Combat Outpost Margah and usually involved two to four rockets each, officers said. The incoming fire has continued through recent days, including an attack last Friday that set buildings ablaze at Forward Operating Base Tillman. The data release does not include attacks against American military positions in provinces other than Paktika or against Forward Operating Base Lilley, in the same province, which is used by the C.I.A. But it does include attacks from several insurgent positions just inside Afghanistan, some within 200 yards of the border, from where rocket crews fire and then rush to Pakistan. There were at least 102 of these so-called close-border attacks against the same outposts since May, including one on Oct. 7 that the American military called the largest and most coordinated insurgent operation in the province since 2009. Another officer, who analyzed each incident, said attacks often come from positions next to Pakistani military or Frontier Corps border posts. He said there has been no sign of Pakistani units trying to stop the firing, or of willingness to help American units identify who is shooting at them. He offered a commonly held assessment: They are getting help, the officer said of the insurgents. Its PakMil, he added, using the acronym for Pakistani military. Asked what evidence supported this claim, he said: Contact with the PakMil when these incidents are going on is often nonexistent. We usually cant get a hold of these guys. When we do get a hold of these guys, they say they are not aware or cant see it. Looking at the terrain, it is very hard to believe. Other officers added that the Americans have been lucky so far. None of the rockets have wounded an American soldier since July 1, roughly when the current unit began to arrive in the province. Eventually were going to get hit, and were going to lose soldiers, one said. This officer was especially frustrated, he said, because an operation planned for early October, in which soldiers intended to sweep on foot through a firing position on Afghan soil beside the border, was canceled by senior officers in Bagram, where the regional American command is located. When taking fire from Afghanistan, they said, they return fire with barrages of high-explosive and white phosphorus artillery rounds. When receiving fire from Pakistan, they said, they do not return fire with white phosphorus and fire far fewer high-explosive rounds. Attack helicopters and aircraft are also less likely to fire ordnance the closer the firing position is to the border, they said, even if it is on the Afghan side. And Colonel Bohnemann noted a complicated history. Afghan units have patrolled to the border, he said, and then been fired on by Pakistani military units who claimed they mistook the Afghans for insurgents. That fighting included Pakistani artillery fire. The risk of having an American patrol face similar fire has been reasonable grounds for caution when planning sweeps near the border, and when returning fire over it, he said.