Here is a look at al Qaeda in the Arabian Peninsula (AQAP) and Ansar al-Sharia militants in Yemen:
* When Islamists seized control of towns in the southern province of Abyan in May 2011, they identified themselves as Ansar al-Sharia (Partisans of Islamic Law). Sheikh Abu Zubayr Adil bin Abdullah al-Abab, AQAP's chief religious figure, had in the previous month announced that "the name Ansar al-Sharia is what we use to introduce ourselves in areas where we work to tell people about our work and goals".
* The group released newsletters and videos via its news wire service, the Madad News Agency, and communicated with the media via a spokesmen. It described the towns it took over as Islamic "emirates", and meted out some radical Islamist punishments such as chopping hands off of thieves, locals said.
* Then-President Ali Abdullah Saleh was grappling with mass popular protests at the time and he held up the Islamists' sudden success as an example of what al Qaeda would do unleashed if Yemen slipped further into chaos. But opponents suspected he had given a signal to militants, with whom the government had lines of communication, to make their move because he felt it would strengthen his case with the West for political survival.
* Last May, after Saleh's ouster, the Yemeni army launched a large-scale U.S.-backed offensive against Ansar al-Sharia. The army ejected militants from their main strongholds in June and regained control of Jaar, Zinjibar and Shuqra, the main towns they had controlled.
* The group has now largely disappeared as a name in usage, and diplomats in Sanaa and analysts say they view it as al Qaeda under another name. Some analysts had suggested the group was part of a coalition that included AQAP.
* In 2009, Al Qaeda's Yemeni and Saudi wings merged into a new group, al Qaeda in the Arabian Peninsula, (AQAP) based in Yemen. AQAP Yemeni leader Nasser al-Wuhayshi, also known as Abu Basir, was once a close associate of Osama bin Laden, whose father was born in Yemen. Yemen said last month that its forces had killed AQAP's deputy leader, Said al-Shehri. But Shehri later issued an audio tape saying he was alive.
* AQAP set out its aims in a May 2010 statement as "the expulsion of Jews and crusaders" from the region, establishing a Sunni Muslim state ruled by sharia (Islamic law) and the liberation of Muslim lands.
Sources: Reuters/Janes World Insurgency and Terrorism/here://www.foreignpolicy.com
(Reporting by David Cutler, London Editorial Reference Unit; Editing by Mark Heinrich)