(CNN) -- Osama bin Laden stresses the importance of martyrdom for Muslim causes in a videotape that purportedly contains a 50-second message from the al Qaeda leader.

Osama bin Laden appears on videotape saying that martyrdom is a worthy goal for every Muslim.

The 40-minute videotape, whose audio was being translated from Arabic by CNN, was intercepted before it was to appear on several Islamist Web sites known for carrying statements from al Qaeda and other radical groups.

The videotape, titled "A Special Surprise from As-Sahab. Heaven's Breeze Part I," was made in the last four weeks, but the clips appear to be old, said Octavia Nasr, CNN's senior editor for Arab affairs. There is no indication of where it was shot, and CNN cannot verify its authenticity.

"We're aware of the tape," a government official, who didn't want to be identified, told CNN. The official agreed that the tape's content is not necessarily new.

"There has not been, over time, a one-to-one correlation between release of a tape and any significant operation or attack afterward," the official added.

Bin Laden, with a bodyguard standing directly behind him, is looking down slightly in the video, appearing to address an audience below, which is unseen. Watch the al Qaeda leader »

He says that the Prophet Mohammed wanted to be a martyr, and that is a worthy goal for every Muslim.

"So be alert, be wise and think. What is this status that the best of mankind wished for himself? He wished to be a martyr. He himself said, 'By him in whose hands my life is! I would love to attack and be martyred, then attack again and be martyred, then attack again and be martyred.'

"So this whole broad life is summarized by him who was inspired by God, the Lord of the heavens and earth, praised and exalted is he. This glorious prophet who was inspired by God summarized this entire life by these words. He wished upon himself this status. Happy is the one who was chosen by God as a martyr."

Bin Laden was one of several men appearing and speaking on the tape. They include Abu Musab al-Zarqawi, the leader of al Qaeda in Iraq who was killed in a U.S. airstrike June 7, 2006.

The video was branded by As-Sahab Media, the company that traditionally handles al Qaeda communications to the public.

The environment shown is similar to that on releases made before the September 11, 2001, terror attacks, in which bin Laden is seen in the company of some of the hijackers, Nasr said.

Some of the backdrops also resemble those shown in videos when the U.S. attacks against the Taliban in Afghanistan began not long after the 9/11 attacks, she added.

The last time a recording of bin Laden was made public it was an audiotape, with an Arabic transcript, released on June 30, 2006.

For several weeks, radical Islamist Web sites have been announcing that there would be "good news soon from Sheikh Osama bin Laden." E-mail to a friend

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