For most people, al-Qaeda and its chief Osama bin Laden are inextricably linked to Afghanistan but it was in Yemen that al-Qaeda's war against the West began.
Praveen Swami, Diplomatic Editor
Published: 8:35PM BST 29 Oct 2010
It is bin Laden's ancestral home and in December, 1998, it was where a little-known Islamist group responded to his calls for attacks on US and British targets by kidnapping sixteen tourists. Three British citizens and one Australian were killed when Yemeni forces stormed the kidnappers' safe house, 175 miles south of the Yemeni capital of Sanaa.
Since then al-Qaeda has branched into a global network and built new terror training camps and bases across Asia.
But now it has returned and Yemen is once again emerging as the global jihadist movement's new citadel.
Increasingly plots targeting the west have had a Yemen connection - often involving al-Qaeda operatives inspired and trained by the organisation's key leader, Anwar al-Awlaki, who was raised in Yemen, educated at US universities, a mentor for three of members of the al-Qaeda hijack squad which carried out the 9/11 attacks.
No hard data exists on just how many terrorists al-Qaeda has at its disposal in Yemen, but most intelligence estimates run to several hundred. Most are Yemeni, but authorities in that country have arrested at least 50 foreign nationals linked to al-Qaeda - among them, British, US, French and Malaysian citizens.
Jonathan Evans, the director-general of the Security Service, said last month that threats to the UK are increasingly emanating from Yemen and Somalia - not just the war-torn lands along the Pakistan-Afghanistan border.
Yemen has been engaged in a bitter battle against these forces, using its air force and artillery to target the al-Qaeda bases. Colonel Mohamed al-Khodr, the head of security in the troubled South Yemen province of Abyan said earlier this month that his country's forces were "engaged in what amounts to guerrilla war". He admitted that "we have not managed to win the battle and are facing difficulties". More than 50 Yemeni security force personnel have been killed by al-Qaeda this year
Yemen's al-Qaeda faction is known as al-Qaeda in the Arabian Peninsula, and was yesterday accused by US Homelands Security of involvement in the cargo plane terror alert. It is led by is Nasser Abdul Karim al-Wuhayshi, a former personal assistant to bin Laden. Al-Wuhayshi was arrested by Iranian authorities and extradited to Yemen, but escaped from prison in 2006.
Al-Qaeda in the Arabian Peninsula has demonstrated a high degree of ability to hit Yemen were it most hurts - hitting the diplomats, aid workers and tourists who are so essential to the country's cash-strapped economy. Earlier this month, al-Qaeda terrorists targeted the deputy chief of the UK's embassy in Sana'a, Fionna Gibb. In April, an al-Qaeda suicide bomber almost succeeded in assassinating Tim Torlott, Britain's ambassador to Yemen. Last year, the jihadist group targeted a convoy bearing the families of four South Koreans it had killed in an earlier suicide attack.
The group is responsible for the publication of the al-Qaeda magazine which gives advice to would-be militants. The latest edition included a section on how to mow people down with a pickup truck and other tips on how to kill Americans. It indicated that the terrorist network was moving away from terror "spectaculars" towards smaller scale operations.
Yemen's evolution as a jihadist launch-pad dates back to the 1980s, when hundreds of its citizens joined in the jihad against the Soviet Union's forces in Saudi Arabia. Though born to a Syrian mother, and raised in Saudi Arabia, bin Laden's father Mohammad bin Laden hailed from the mountainous Hadramawt-region village of Ribaat Bashen, and the al-Qaeda chief often said he dreamt of one day returning there.
The Afghan jihad veterans played an important role in Yemen's political life after they returned. In 1994, Ali Abdullah Saleh, Yemen's president, recruited their services to defeat left-wing separatists in the south; many later received government handouts and rewards. Sheikh Abdulmajid Zindani, a former bin Laden associate, remains among the country's most influential people.
British nationals played a key role in some of al-Qaeda's first attacks in Yemen. In December 1998 and January 1999, British nationals belonging to an organisation calling itself the Supporters of Shariah (Islamic Law) were convicted of attempting to blow up British targets in Yemen. The organisation was led by Mustafa Kamel Mustafa - a man better known by his jihadist nom de guerre, Abu Hamza.
The son of an Egyptian military officer, and a former nightclub bouncer, al Masri discovered radical Islamism while he was a student at Brighton Polytechnic.
He is currently in prison in Belmarsh awaiting the outcome of a US request for his extradition on terrorist charges.