Ayman al-Zawahiri, Al Qaeda's [Images] second most powerful leader after Osama Bin Laden, might be critically wounded and possibly dead, according to a media report.

The CBS News reported that it had obtained a copy of an intercepted letter, which urgently requests a doctor to treat al-Zawahiri. The Al Qaeda leaders are believed to be hiding somewhere in Pakistan's tribal areas.

The letter, reportedly written by Pakistani Taliban chief Baitullah Mehsud, refers to al-Zawahiri by name and states that he is in 'severe pain' and his injuries are infected. CBS News said the Taliban logo and Mehsud's seal on the letter had been "confirmed by experts as legitimate".

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The letter is dated July 29, a day after a United States missile strike killed al-Qaeda weapons expert Abu Khabab al-Masri and five other Arabs in Pakistan's South Waziristan tribal region.

A counter-intelligence expert and other American officials told the channel that the US is looking into reports that al-Zawahiri is dead.

However, Pakistani military spokesman Major General Athar Abbas told TV news channels that there was 'no evidence or reliable information' about al-Zawahari's death.

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Husain Haqqani, Pakistan's Ambassador to the US, told CNN that his country was unable to confirm or deny the report. "We are looking into the reports and will comment only after we have solid evidence either way," he said.

A US$ 25 million reward has been offered for the 57-year-old al-Zawahiri. He narrowly escaped death in an attack in the Tora Bora region of Afghanistan in 2001 that left his wife and children dead.

Al-Qaeda [Images] reported on Islamist websites this week that a US air strike killed Abu Abdallah al-Shami, a leader who escaped from a US prison in Afghanistan in 2005.

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