Sanaa---Powerful armed groups have sidelined Yemen's government ever since a 2011 popular uprising forced long-time president Ali Abdullah Saleh to step down.
Shiite militiamen and Sunni extremists have sought to exploit the power vacuum, as escalating violence and political chaos grip Yemen.
- The Huthis -
The Shiite Huthi militia, also known as Ansarullah (Supporters of God), have long complained of marginalisation by authorities in Sanaa.
They hail from the Zaidi sect, an offshoot of Shiite Islam that makes up approximately one-third of Yemen's Sunni-majority population.
Their strongholds lie in northern provinces bordering Sunni powerhouse Saudi Arabia and they are accused of receiving support from Shiite Iran.
North Yemen was a Zaidi imamate until a 1962 coup turned the country into a republic.
Badreddin al-Huthi, who formed the "Faithful Youth" political movement in 1992 to fight discrimination, is regarded as the spiritual leader of the Huthis, who have taken his name.
His son Hussein led a nearly three-month uprising in Saada province before the army killed him in 2004.
Ansarullah is now led by Hussein's brother, Abdulmalik.
Six wars fought with the central government between 2004 and 2010 killed thousands of people before a truce was signed.
After months of clashes with the Sunni Islamist party Al-Islah last year, the Huthis took control of the capital on September 21.
They are thought to be backed by forces loyal to Saleh, who stepped down in early 2012.
- Al-Qaeda -
Al-Qaeda in the Arabian Peninsula (AQAP) is regarded by the United States as the extremist network's deadliest branch.
It was formed in 2009 when Al-Qaeda in Yemen -- whose biggest attack was the 2000 bombing of the USS Cole in Aden harbour that killed 17 American sailors -- merged with its Saudi counterpart.
AQAP fighters have repeatedly attacked Yemeni security forces and been targeted by scores of US drone strikes.
From strongholds in southern and southeastern Yemen, AQAP has launched a series of raids on major state institutions such as the defence ministry and intelligence headquarters.
The group abducts foreigners, including US journalist Luke Somers and South African teacher Pierre Korkie, killed by their captors when American commandos stormed an AQAP hideout last year.
AQAP also claimed responsibility for the deadly January 7 attack in Paris on French satirical magazine Charlie Hebdo, targeted for its cartoons of the Prophet Mohammed.
With state institutions weakened, AQAP has become the only force capable of resisting the advance of Ansarullah.
Sunni tribes, hostile to a Huthi advance into their provinces, have teamed up with Al-Qaeda against the militia, with the government mostly standing by.
Since September, AQAP has claimed several attacks on the Huthis, including the killing of 49 people in the central province of Ibb in December and one in October that left 47 dead in Sanaa.
AFP
