Al-Qaeda, the organisation once led by Osama Bin Laden, may have underground cells in dozens of countries, but its main areas of activity, and those of some of its affiliates, are detailed below.
Afghanistan and Pakistan
Al-Qaeda was originally set up in Peshawar in 1988, and the tribal areas of the Afghanistan-Pakistan border are the most well known of al-Qaeda strongholds.
The area is also believed to contain training areas, although the CIA states that US drone attacks have taken a significant toll on al-Qaeda and the Taliban here.
Al-Qaeda's co-operation with the Taliban meant that Osama Bin Laden was given sanctuary in Afghanistan prior to the September 11 attacks on New York and Washington.
Having left Afghanistan in 2001, as a result of the US invasion, Bin Laden was ultimately found and killed in Abbottabad, Pakistan, in 2011.
Ayman al-Zawahiri, one of the most senior al-Qaeda leaders, was last seen in Afghanistan in October 2001, and before Bin Laden's death was thought to be hiding in the Afghan-Pakistan border region.
Allies of al-Qaeda in Pakistan include Lashkar-e-Jhangvi and Lashkar-e-Taiba, who may have helped hide senior al-Qaeda figures. Lashkar-e-Taiba founder Hafiz Mohammad Saeed helped Bin Laden set up al-Qaeda in 1988.
The Haqqani network and other Pakistani Taliban groups are also allies of al-Qaeda, as is the Islamic Movement of Uzbekistan. Like al-Qaeda it found sanctuary in Pakistan's border areas after the US invasion of Afghanistan in 2001.
Arabian Peninsula
Al-Qaeda in the Arabian Peninsula covers Saudi Arabia and Yemen and came about in 2009 when militant groups from the two countries joined forces.
The group's main aims are the overthrow the governments of Saudi Arabia and Yemen, and the removal of Western influence in the Gulf.
They have been linked to an attempt to blow up a trans-Atlantic flight to the US in 2009.
Earlier attacks in the region include bombing a residential compound in Riyadh in 2003, which killed 34 people, and the attack against the destroyer USS Cole in Aden harbour in 2000, which killed 17 US service personnel.
East Africa
Al-Qaeda has long had a presence in East Africa, the scene of the attacks on the US embassies in Nairobi, Kenya and Dar es Salaam, Tanzania.
The attacks of August 1998 were carried out by fighters from Egypt, Sudan, Kenya, Tanzania, Comoros and Saudi Arabia. Some of these underwent training in Somalia, where they fled afterwards.
The insurgent group al-Shabab, which has links to al-Qaeda and works with foreign jihadists, controls much of southern and central Somalia. In some areas, it has carried out horrific punishments, such as the stoning to death of a young woman, who claimed she had been raped, for adultery. In 2009 US forces killed Saleh Ali Saleh Nabhan, a top al-Qaeda operative accused of links to the 1998 embassy bombings, in a raid in Somalia.
In 2010, suicide bombers killed at least 74 people in Uganda in revenge for that country sending troops to help Somalia's UN-backed government battle al-Shabab.
Asia-Pacific
In this region, two groups thought to have links to al-Qaeda are based in Indonesia and the Philippines.
Jemaah Islamiah, based in Indonesia, is believed to have been responsible for the attacks on nightclubs in Bali in 2002, which killed over 200 people.
Other targets of the group, whose history goes back to the 1980s, have included Christians in eastern Indonesia and the tourist industry.
The Abu Sayyaf group, based in the southern Philippines, is said by the United Sates to have links with the al-Qaeda network. Involved in multiple kidnaps for ransom, its main aim is for an independent Islamic state in Mindanao and the Sulu islands.
Europe
Al Qaeda's presence in Europe is not as structured as elsewhere. Counter-terrorism officials describe militants here as inspired by al-Qaeda, but not always directed by them.
Alleged bomb plots have been foiled as recently as April 2011, with German police arresting three suspected al-Qaeda members whom they believed posed an imminent threat.
Other threats were uncovered in Europe in September 2010, when Western intelligence sources said they had disrupted a plot to seize and kill hostages in the UK, France and Germany.
In 2007 Belgian officials said they had foiled a plot to free a Tunisian al-Qaeda member jailed in Belgium. Fourteen alleged militants were arrested.
Responsibility for the Madrid train bombings of March 2004, which killed nearly 200 people, was claimed by groups with links to al-Qaeda. The 7 July 2005 attacks on London, which killed 52 people, are also believed to have had al-Qaeda links.
The al-Qaeda cell blamed for 9/11 was based in Hamburg. A mosque frequented by the 9/11 plotters was eventually closed in 2010, because it was allegedly still hosting extremists.
Iraq
Al-Qaeda in Iraq was formed in 2004, the year after the US invasion, when the Jordanian militant Abu Musab al-Zarqawi pledged allegiance to Osama Bin Laden. It is also known as al-Qaeda in Mesopotamia.
Al-Qaeda here has been responsible for many attacks, but the group's capacity diminished from 2006-7, when Sunni Arab leaders turned on them, and the US military launched its troop surge.
But al-Qaeda in Iraq remains operationally active.
Al-Zarqawi himself was killed in June 2006. He was succeeded by Abu Hamza al-Muhajir, whose death was reported in 2010.
North Africa
In this region al-Qaeda has perhaps been most active in Algeria, but it has spread right across the Sahara Desert to Mali and Niger, where it has taken hostage several Europeans, some of whom have been killed. Tunisia, Morocco and Mauritania have all battled Islamists or al-Qaeda inspired groups.
In 2006 an Algerian group called the Salafist Group for Preaching and Combat (Groupe Salafiste pour la Predication et le Combat, or GSPC), aligned itself with Osama Bin Laden.
The following year it changed its name to the Al-Qaeda in the Islamic Maghreb. The leader of the group is Abou Mossab Abdelwadoud.
The group's target list includes Western interests, soldiers, foreign oil workers, UN staff and US diplomats.
A Moroccan group was responsible for the 2004 train bombings in Madrid, which killed 191 people.
