On Wednesday, Afghanistan's foreign ministry issued an angry warning to Pakistan after claiming that about 300 rockets had been launched across the Pakistani border into the Nuristan and Kunar provinces of Afghanistan, killing an unspecified number of civilians.

Pakistan responded that its government was targeting insurgents belonging to Tehreek-e-Taliban, a designated terrorist group, not Afghan civilians.

But last week's cross-border fire was far from an isolated incident.

In May, U.S. Apache helicopter crews were fired upon by Pakistan, and they returned fire, wounding at least two Pakistani soldiers, International Security Assistance Force officials said. The American aircraft were in Afghan airspace, according to an ISAF spokesman. Pakistan accused the helicopter crews of crossing the border.

That encounter was reported by ISAF, but many others are not, U.S. and Afghan officials told The Washington Examiner.

"We're not allowed to return fire to coordinates inside the Pakistan border," a military official told The Examiner on the condition he not be named. "We know it's the Pakistani military in many cases. Pakistan has been instigating, aiding Haqqani, and has been purposefully working to turn back any gains ISAF has made in the region."

Another U.S. official said, "This has been going on for some time, but because it's so sensitive it has been kept relatively quiet."

"The situation is very fluid," said one Afghan official. "They have been firing across the border. The incidents have been increasing and [Afghan] forces fire back in response."

Tension between the U.S. and Pakistan has recently reached levels not seen since the countries were thrown into the common cause of defeating al Qaeda and the Taliban after the Sept. 11, 2001, terrorist attacks. Earlier this month, Adm. Mike Mullen, the just-retired chairman of the Joint Chiefs of Staff, accused the Haqqani family network of being a "veritable arm" of Pakistan's military and intelligence service.

Support for active U.S. military operations against the Haqqani organization inside Pakistan has been growing in U.S. military and political circles, according to numerous reports.

Afghan forces dealt a blow to the Haqqani family late last week by capturing Haji Mali Khan, uncle of network leaders Siraj and Badruddin Haqqani and a senior Haqqani commander in Afghanistan. He was apprehended after he traveled from a stronghold in Pakistan into Afghanistan, officials said.

But that is, at best, a morale-building strike against the Haqqani network, which is estimated to control as many as 15,000 fighters.

It has been a tough year for U.S.-Pakistani relations. Pakistan arrested CIA contractor Raymond Davis in January after a deadly shooting that he said was in self-defense during a robbery; the case festered until Davis was released in mid-March. Then the U.S. mounted an elaborate mission to kill Osama bin Laden deep inside Pakistan without telling that country's leaders.

Bruce Riedel, a former CIA officer and senior adviser to three U.S. presidents, said that Pakistan believes the U.S. is ready to call it quits in Afghanistan, and Pakistan is trying to "push us out faster."

Pakistan has increased the use of its Afghan proxies to carry out terror operations in an effort to exhaust U.S. and European patience at home, knowing that President Obama has called for U.S. forces to withdraw by 2014. Pakistani military leaders believe "they can weather the blowback from Washington" because the U.S. needs Pakistan's logistical supply lines stretching from Karachi to Kabul, Riedel said.

At the same time, he said, Pakistan is preparing to replace the billions of dollars of critical military aid it has been receiving from the U.S. by courting China and soliciting help from Islamic ally Saudi Arabia.

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scarter@washingtonexaminer.com

Sara A. Carter is The Washington Examiner's national security correspondent. She can be reached at scarter@washingtonexaminer.com.