Al-Qaeda in the Arabian Peninsula, which is reported to have trained one of the two suspects in the deadly attack on French magazine Charlie Hebdo, is seen by Washington as the jihadist network's most dangerous branch.
It was formed in January 2009 as a merger of the Yemeni and Saudi branches of Al-Qaeda and is led by Nasser al-Wuhayshi.
AQAP has a record of launching attacks far from its base in Yemen, including a bid to blow up a US airliner over Michigan on Christmas Day in 2009.
The group recently called for its supporters to carry out attacks in France, which is part of a US-led coalition conducting air strikes against Islamic State group jihadists in Iraq and Syria.
AQAP's English-language propaganda magazine "Inspire" has urged jihadists to carry out "lone wolf" attacks abroad. In 2013 it named Charlie Hebdo cartoonist and editor-in-chief Stephane Charbonnier among its list of targets.
Charbonnier was one of 12 people killed in Paris on Wednesday by two gunmen who stormed the magazine's offices.
In 2009 an AQAP suicide bomber tried to assassinate Saudi Prince Mohammed bin Nayef, the oil-rich kingdom's current interior minister who had led a crackdown on the militant group between 2003 and 2006.
The attacker managed to infiltrate Prince Mohammed's security in Jeddah and detonate explosives planted inside his body. The prince escaped with light wounds and the bomber was the only fatality.
In November 2010, the group claimed responsibility for sending parcel bombs to the United States and putting a bomb aboard a UPS cargo plane that crashed two months earlier in Dubai.
It took advantage of the weakness of Yemen's central government during an uprising in 2011 against now-ousted president Ali Abdullah Saleh to seize large swathes of territory across the south.
But after a month-long offensive launched in May 2012 by Yemeni troops, most militants fled to the more lawless desert regions of the east towards Hadramawt province.
Since then, AQAP has regularly carried out deadly attacks against Yemeni security forces and, more recently, has claimed a series of bombings against Shiite Huthi militiamen in the capital Sanaa and central provinces.
- Drone strikes -
The US has launched scores of drone strikes on AQAP targets in Yemen, including an attack that killed US-born American radical Islamist cleric Anwar al-Awlaqi in September 2011.
Months later, Yemeni Al-Qaeda leader Fahd al-Quso, who was believed to have helped mount a deadly attack on a US warship in a Yemeni port in 2000, was killed in an air raid blamed on the US.
In July 2013, AQAP confirmed the death in a US drone strike of its deputy leader Saeed al-Shehri, a former Guantanamo Bay prisoner in Cuba who had undergone rehabilitation in Saudi Arabia after his release.
The first known attack of Al-Qaeda in Yemen dates back to 1992, when bombers hit a hotel that formerly housed US Marines in the southern city of Aden, in which two non-American citizens were killed.
In 2000, an Al-Qaeda suicide attack on the naval destroyer USS Cole in Aden killed 17 US military personnel.
Two years later, a bomb-laden boat struck the French-owned oil tanker Limburg off the coast of Yemen. Al-Qaeda claimed responsibility for the attack that killed a Bulgarian sailor.
Wuhayshi in July 2011 reaffirmed the group's allegiance to Ayman al-Zawahiri, head of the worldwide Al-Qaeda network since the death of Osama bin Laden in May 2011.