Osama bin Laden has issued a letter urging Pakistani Muslims to defend Islam against what he described as a Christian crusade, al-Jazeera satellite television has reported.
The television showed a picture of the letter written in Arabic which it said was signed by bin Laden. A copy of the letter was not immediately available.
Osama bin Laden called on Muslims in Pakistan to stand in the face of what he called a Christain crusade against Islam, a Jazeera newsreader quoted the letter as saying.
"Muslims in Afghanistan are being subjected to killing and the Pakistani government is standing beneath the Christian banner", the letter was quoted by the newsreader as saying.
Earlier it was reported that about 1,000 armed Pakistani tribesmen had crossed into Afghanistan to fight with the Taliban against the US.
They crossed the border at Bajaur agency in North West Frontier Province, a witnesses said. Taliban vehicles were waiting on the other side of the border in Afghanistan's Kunar province.
The fighters were led by Maulana Mohammad Ismail, leader of the radical Tehreek Nifaz-e-Sharia Mohammadi.