Algerian jihadist Mokhtar Belmokhtar, whose group occupied northern Mali in 2012, pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri in a statement posted Wednesday on Islamist websites.

Belmokhtar was a leader of Al-Qaeda in the Islamic Maghreb (AQIM), which, along with other armed Islamist groups, took advantage of a military coup in 2012 to occupy northern Mali before being driven out by French and African troops.

The elusive Islamist, who staged the deadly siege of an Algerian gas plant last year, was thought to have been killed in Mali, but security sources told AFP in mid-April he had moved into Libya and remained active.

"We declare our faith in the policies of our emir, Sheikh Ayman al-Zawahiri... because we are convinced of the fairness of his approach," Belmokhtar said in the statement.

He specifically mentioned Zawahiri's latest comments on in-fighting between Islamist rebels in Syria that has killed hundreds since January.

Last year Zawahiri ordered the Islamic State of Iraq and the Levant (ISIL) to confine its activities to Iraq after it was accused of widespread abuse against Syrian civilians and rival rebels.

Later, Zawahiri declared Al-Nusra Front to be the official Al-Qaeda affiliate in Syria.

In more recent comments, Zawahiri called for unity among Islamists fighting in Syria to topple the government of President Bashar al-Assad.

The one-eyed Belmokhtar split from AQIM in 2013 to form his own group, the Signatories in Blood, and masterminded the deadly raid against Algeria's In Amenas gas plant in which 38 hostages were killed in a four-day siege last year.

The attack was said to have been carried out in retaliation for the French-led military intervention in Mali.

The United States designated Belmokhtar's group as a terrorist organisation in December, and the State Department is offering a $5 million reward for information leading to his capture.

In mid-April Mali's President Ibrahim Boubacar Keita said that Belmokhtar -- who had also fought the Soviets in Afghanistan during the 1990s -- was "a threat" to regional security.