Ayman al-Zawahiri, the Egyptian surgeon-turned-jihadist ideologue, has been appointed the new chief of al-Qaeda to succeed the group's slain leader Osama bin Laden, according to a statement posted on militant websites.

Al-Zawahiri, 59, one of the founders of the al-Qaeda, has played a defining role in the militant group for more than a decade as bin Laden's deputy. Even before the announcement, he had been widely regarded as the organisation's de facto leader and public face.

The announcement, dated June 2011 but which surfaced today on the jihadist sites, said the decision to appoint al- Zawahiri, who is carrying a USD 25 million reward on his head, was made to pay respect to the "righteous martyrs" and to honour the legacy of bin Laden.

"Hereby the General Command of the Qaeda al-Jihad -- and after the end of the consultations -- we declare that Sheikh Dr. Abu Muhammad Ayman al-Zawahiri (May God bless him) will take over the responsibility of command of the group," CNN quoted the statement as saying.

He is believed to run al-Qaeda operations from the Pakistan-Afghanistan border region.

Al-Zawahiri had issued a eulogy for bin Laden last week saying al-Qaeda's leader had terrified the US when he was alive and would continue to do so in death.

He appeared in a white Arab robe and turban, a Kalashnikov at his side, in the 28-minute video posted on jihadist online forum.

"We will pursue the jihad until we expel the invaders from Muslim lands," he had said.

Bin Laden was killed in a US raid on his compound in Abbottabad near Islamabad on May 2.

The statement also said the group will not shift its policy and pledged its support to, among others, Taliban chief Mullah Omar.

It, however, makes no mention of the pro-democracy uprisings that have roiled several Arab countries and forced the exit of some longtime leaders.

Last month, Abu Al-Fida, a top commander of Al-Qaeda in the Arabian Peninsula (AQAP), had said al-Zawahiri is the "best candidate and right person" to succeed bin Laden.

"Al-Zawahiri is the best candidate and he is the right person to take over. All wings of al-Qaeda would approve of him and all Jihadist movements trust him greatly," he said.

Al-Zawahiri, the second and last "emir" of the Egyptian Islamic Jihad, an affiliate of al-Qaeda, was wanted in the US even before the 2001 attacks targeting New York's World Trade Centre and the Pentagon, which killed more than 3,000.

He was indicted in absentia in 1999 for the August 1998 bombings of US embassies in Tanzania and Kenya that killed 224 people, and was also considered the mastermind of the October 2000 bombing of the USS Cole in Yemen, which killed 17 sailors.

Born into a wealthy family in Cairo, al-Zawahiri is a physician and founding member of the Egyptian Islamic Jihad (EIJ), a militant group that opposed the then secular Egyptian government of Hosni Mubarak and sought its overthrow through violent means.

Like bin Laden, al-Zawahiri also went to Afghanistan during their fight against the Soviets, although he was there primarily to offer his medical expertise.

By the 1990s, he again refocused his attention on undermining and attacking the Egyptian government and, eventually, the US.