ISLAMABAD - The US-led coalition hunting Osama bin Laden and his former chief protector Mullah Mohammad Omar said on Wednesday it was unaware if the two men were still in Afghanistan or had slipped away, but the search would go on.

"We don't know," coalition spokesman Kenton Keith said about the whereabouts of the fugitives at a news briefing in Islamabad as US jets prowled the skies above Afghanistan, hunting new targets in the 102-day-old war against the elusive Saudi-born militant Bin Laden.

"I can assure you that just because they haven't been caught ... doesn't mean that the coalition has relaxed its efforts, nor have the authorities and the military units in Afghanistan," he said.

"On land, in the air and on sea, Osama bin Laden and Mullah Omar are being sought, and that process will continue until they are found," said Keith.

He was asked about recent media reports that Mullah Omar, the supreme leader of Afghanistan's collapsed Taliban movement, had nearly been caught but escaped and that Bin Laden could have escaped by sea via Pakistan to an unknown destination.

"We certainly don't know where they are," Keith said.

"It is conceivable that some kind of escape by sea has taken place. It is also equally conceivable that they are still in Afghanistan and still in the region we have been looking for them. It's not easy to cover all of that territory."

In Afghanistan, US officials said their planes, which in recent days levelled about 60 buildings and closed entrances to dozens of caves in the Zhawar Kili region of eastern Afghanistan, were looking for fresh targets and acting to prevent al Qaeda and Taliban forces from regrouping.

Last month, the coalition and anti-Taliban Afghan forces bombed out the eastern Tora Bora cave complex, killing or driving out hundreds of militants of Bin Laden's al Qaeda network but no trace of their leader was found.

Keith said the difficulty in finding Mullah Omar, widely believed to be hiding somewhere in his former powerbase in southern Afghanistan, was the difficult terrain and it was "the heartland of the area that bred and sustained" him.

"It is not surprising that he is elusive in that area. But it is not infinite and he will be caught," he said.

Keith said coalition forces were tying up the loose ends of the military campaign after routing al Qaeda and overthrowing the Taliban regime.

Keith said al Qaeda was still capable of striking at the United States.

"Al Qaeda is not just that group of people who ... had formed themselves as a military force in place in Afghanistan, but al Qaeda is groups of people allied with that institution and allied with men who led it, who are all over the world. "So yes I do think that al Qaeda is capable of striking at the US, and striking at any other country for that matter," he said. - Nampa-Reuters