New York: The US security forces appear to have concluded that Osama bin Laden is probably still alive and is somewhere on the border between Afghanistan and Pakistan.

The assumption driving the manhunt is that Osama and his top lieutenant, Ayman al- Zawahiri, are alive, some American officers, speaking privately to a newspaper said.

The officers cited Afghan and Pakistani intelligence reports, mostly sketchy, that have spoken of bin Laden and an entourage of several dozen moving more than once since the American bombing of the Tora Bora mountains late last year.

Some of those reports have suggested that the fugitives may have moved through the mountains on horseback, probably on cloudy nights to elude aerial surveillance, the officers said.

The region being searched covers four provinces, Kunar, Nangahar, Paktika and Paktia, and the adjoining Pakistani tribal areas, the paper said.

At the time of the biggest American ground battle at the Shah-i-Kot Valley, 160 km South West of Kabul, the US officers told the 'New York Times' that al-Qaida and Taleban fighters might be protecting bin Laden and Zawahiri. But after the battle, no trace of the al-Qaida leaders was found. The US military spokesmen said some al- Qaida men appeared to have slipped through mountain passes toward Pakistan, the paper added.

The special forces units deployed to bases like the one at Asadabad in Afghanistan are working on the assumption that applying pressure on any possible hideout is the best means of exposing their quarry, a spokesman for the American Command, Lt Col Roger King, was quoted by 'The Times' as saying.

"I'd say it's a reasonable conclusion that we feel that if bin Laden is alive, we're providing enough pressure to make sure he keeps moving," King said adding, "It's easier to spot a moving target."

PTI