Cross-border attacks emanating from Pakistan against US-led forces in Afghanistan have increased since the US raid that killed Osama bin Laden in Pakistan, the Pentagon said Monday.

Asked if there was a recent rise in artillery or rocket fire across the border into Afghanistan, press secretary George Little told reporters in an email: "This summer, June-August, we did see an increase in cross border incidents."

The Pentagon offered no other details and did not link the trend to the May raid by Navy SEAL commandos deep inside Pakistan that took out Al-Qaeda's leader.

But US soldiers at bases in Afghanistan's eastern Paktika province told the New York Times that rocket fire had dramatically increased from Pakistani territory since May.

It was unclear if the fire, usually 107mm rockets, was the result of an emboldened insurgency, retaliation by the Pakistani military or some mixture of both, the Times reported Monday, quoting US military officers.

In some cases the rocket fire came from insurgent positions just inside Afghanistan, with crews then rushing back across to Pakistan, the newspaper wrote.

There were at least 102 "close-border" attacks against three US outposts in Paktika since May, compared to 13 such incidents during the same period last year, it said.

When contacted by US troops, Pakistani military officers at the border often say they are not aware of the rocket fire or cannot see it, even though the fire is often coming from positions next to Pakistani military or Frontier Corps posts, the Times reported.

Given the degree of sophistication and coordination displayed in the attacks, some US officers strongly suspect the Pakistani military or intelligence service is involved in the rocket fire, the paper said.

The rise in cross-border fire comes amid deep strains in US-Pakistan relations in the aftermath of the Bin Laden raid and following accusations from former top US military officer Admiral Mike Mullen that Islamabad was supporting Haqqani militant attacks on US forces in Afghanistan.