The US is providing behind-the-scene support, including spy satellites, electronic-eavesdropping planes and sophisticated ground sensors, to Pakistani forces combing for Al Qaeda members near the Afghan border, American officials in Washington and the region were on Tuesday quoted as saying.

As part of a broader American offensive just across the rugged boundary in eastern Afghanistan, hundreds of American troops have recently set up what the military calls 'blocking positions' at strategic junctions along the frontier to trap and kill militants fleeing the Pakistani attacks, a media report in New York said.

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A range of American military sensors positioned over Afghanistan are peering across the mountainous border region into Pakistan, the New York Times said. Spy satellites zero in on suspected terrorist camps while US Air Force E-8C Joint Stars ground-surveillance jets and remotely piloted Predator aircraft track their movements.

U-2 spy planes soar high overhead and RC-135 Rivet Joint aircraft scoop up cell phone calls and other electronic transmissions.

In recent weeks and months, the Times said, the American military has provided Pakistani forces with helicopters and specialised training, as well as a range of sophisticated ground sensors that can count vehicles on mountain roads and measure their loads by the vibrations they emit.

The military has some technology that can be used to detect tunnels but it was unclear whether such devices, if available, would have been effective in finding a mile-long tunnel from a mud fortress that Pakistani officials discovered on Monday. It might have been an escape route for militant leaders, the officials said.

"We're trying to meet whatever requests they have," an American military official in the region was quoted as saying.

So far, the paper said, the US has primarily provided technical and tactical assistance to Pakistani security forces. But senior American military officials were quoted as saying that small numbers of commandos attached to Joint Task Force 121, a secret unit made up of military Special Operations forces and Central Intelligence officers, have conducted cross-border operations.

Those commandos, who helped track down and capture Saddam Hussein in Iraq in December 2003, have not been directly involved in the pitched battle between 7,000 Pakistani troops and several hundred militants in a small cluster of villages near the Afghan border, American officials said.

American forces have been authorized to pursue hostile forces into Pakistan from Afghanistan if US troops maintained 'continuous contact' with the fighters, a senior officer with experience in Afghanistan told the Times.