Al-Qaeda leader Osama Bin Laden has called on Pakistanis to overthrow President Pervez Musharraf.
Bin Laden has called for Musharraf's overthrow before
In a new audio tape, Bin Laden promised what he called retaliation for the storming of the radical Red Mosque in the capital, Islamabad, in July.
He said the army operation, in which more than 100 people were killed, made Gen Musharraf an infidel.
The new audio message was heard on the internet over previously released footage of the militant leader.
In the tape, Bin Laden says it is now the duty of Muslims to rebel against what he calls the "apostate leader".
The Pakistani leader is not popular
The storming of the Red Mosque "demonstrated Musharraf's insistence on continuing his loyalty, submissiveness and aid to America against the Muslims... and makes armed rebellion against him and removing him obligatory", Bin Laden said.
The transcript of the tape was released by Laura Mansfield, an American terror expert who monitors militant traffic on the internet.
Bin Laden was quoted as saying on another American web site, Siteinstitute.org, that Gen Musharraf's ministers and soldiers were "all accomplices in spilling the blood of those of the Muslims who have been killed".
"He who helps him knowingly and willingly is an infidel like him."
It is not the first time the al-Qaeda leader has called for the overthrow of Gen Musharraf, a key US ally in the "war on terror".
Since the attack on the World Trade Centre in 2001 he has released a number of videos and audio messages.
But the BBC defence and security correspondent Rob Watson says Osama Bin Laden may well consider this a timely intervention given the current political turmoil in Pakistan and growing unpopularity of President Musharraf.
Indeed, our correspondent says, a poll released earlier this month suggested the Pakistani president was less popular in his own country than the al-Qaeda leader himself.
Even before Bin Laden's latest message, violence by pro-Taleban militants had shot up in Pakistan following the storming of the Red Mosque.
There have been almost daily suicide bombings as well as a number of kidnappings of Pakistani soldiers in tribal areas near the Afghan border and in North West Frontier Province.
The threat from Bin Laden - which referred to radicals in the mosque as "champions of Islam" - was immediately rejected by the Pakistani government.
Osama Bin Laden condemned the storming of the Red Mosque
"We are already committed to fighting extremists and terrorists - there is no change in our policy," chief military spokesman Maj Gen Waheed Arshad told the AFP news agency.
"If someone is hurling threats at us, that is their view. The whole nation is behind us and the Pakistan army is a national institution," he added.
The release of the tape coincided with an announcement by Pakistan's election commission that presidential elections would be held on 6 October.
President Musharraf has said he will give up his post of army chief if he is re-elected by parliament and provincial assemblies for another term.