Pakistani forces are allowing insurgents to launch rocket and mortar attacks on US troops across the border in Afghanistan and may be collaborating with the militants, a US general said Thursday.

The rocket fire targeting American forces often originates within sight of border posts manned by Pakistan's Frontier Corps, said Lieutenant General Curtis Scaparrotti, deputy US commander in Afghanistan.

"In some locations from time to time you will see what just appears to us to be a collaboration... or at a minimum a looking the other way when insurgents conducted rocket or mortar fire in what we believe to be (within) visual sight of one of their (Pakistan military) posts," Scaparrotti told reporters via video link from Kabul.

Soldiers from the Pakistani Frontier Corps are locally recruited and not as highly trained as regular army units, he said.

The cross-border attacks have increased dramatically in eastern Paktika province in recent months, with rocket and other fire four times higher than in previous years, he said.

"We talk very bluntly with our Pakistani counterparts about this," he said.

The rocket fire has coincided with a virtual breakdown in communications between US and Pakistani officers along the border since May, when American special operations forces killed Al-Qaeda chief Osama bin Laden at his compound in Pakistan in a unilateral raid that angered Islamabad.

A year ago, it was common to have radio communications between Afghan and NATO forces and Pakistan's Frontier Corps stationed along the border as well as quarterly planning conferences among officers, the general said.

"About (in) May this past year after the Bin Laden raid, those routine communications just were not available in most cases. We had a difficult time arranging border flag meetings, we had a difficult time arranging border communications back and forth," he said.

But Scaparrotti said he had recently paid a visit across the border to confer with his Pakistani military counterparts and was hopeful that regular communications could be restored along the border.

US officials see the Haqqani network, which uses sanctuaries in Pakistan to stage attacks in eastern Afghanistan and beyond, as a growing threat and allege it has ties to Pakistan's military intelligence service.

NATO-led troops and Afghan forces have targeted the Haqqani militants and their supply routes in a recent major operation near the border, which Scaparrotti said had damaged the insurgent network.

Operation "Knife Edge" involved Afghan army units and elements of three brigades from the NATO-led coalition, as well as Afghan and allied special operations forces carrying out night raids.