"At least for many Pakistanis, the floods have most recently been concern number one," said Prof Pillar, of Georgetown University, who added the al-Qaeda chief "projects a compassionate image" by focusing on social issues.

His aim is "to counteract his loss of support among people who have come to perceive him as an uncaring terrorist who has no hesitation about spilling the blood even of fellow Muslims," he said.

Some US officials have taken pains to highlight the number of Muslims killed by al Qaeda and its offshoots in a bid to sap support for the network behind the September 11, 2001 terrorist strikes on the United States.

Bin Laden, whose latest message avoided direct calls for violence, may also be taking note that militant Islamist groups like Hamas and Hizbollah win public support by providing services, Prof Pillar said.

"If he can't build goodwill by actually providing services like those groups do, he can at least hope to get some mileage out of talking up the subject," he said.

Prof Pillar's comments came after a monitoring group provided what it described as an audio message from bin Laden in which the al-Qaeda chief warned that the number of victims from climate change is "bigger than the victims of wars."

The voice on the message also urged "serious and prompt action to provide relief" to those afflicted by Pakistan's devastating floods, the country's worst environmental disaster.

The recording's focus on Pakistan was notable in that al-Qaeda number two Ayman al-Zawahiri and US-born al-Qaeda spokesman Adam Gadahn both assailed the US ally's response to the flooding.

If authenticated, the tape would be the first time bin Laden has spoken publicly since March 25. The recording was made available by SITE Intelligence Group.