Yemeni former bin Laden aide pledged to fight for generations LONDON (Reuters) - Nasser al-Wuhayshi, the head of Al Qaeda in the Arabian Peninsula (AQAP) whose alleged communications with al Qaeda leader Ayman al Zawahiri sparked a worldwide terrorism alert, is a veteran of global jihad who has promised the West a fight that will last for generations. According to Gregory Johnsen, author of a book on al Qaeda in Yemen, he was born in southern Yemen and left his country for the first time when he went to Afghanistan in 1998 to join al Qaeda. There he acted as Osama bin Laden's aide-de-camp until 2001, when the group was scattered after the U.S.-led invasion of Afghanistan following the September 11 attacks on the United States. He became head of AQAP in 2009, several years after a daring prison break from a jail in Yemen. "Wihayshi has a small ego and a soft voice - but his word carries a lot of influence," Johnsen said on his Twitter feed, @gregorydjohnsen. "Wihayshi is also incredibly patient, which may be a source of frustration and the reason Zawahiri is pushing him to attack," he said. U.S. sources have said that intercepted communication between Zawahiri - believed to be based in Pakistan - and AQAP was one component of a broader pool of intelligence that prompted a threat alert closing numerous U.S. embassies in the Middle East and Africa. That in turn fuelled speculation that Zawahiri, who took over from bin Laden after he was killed by U.S. forces in Pakistan in 2011, had asked AQAP to conduct a major attack against U.S. interests. As a branch of al Qaeda rather than a looser affiliate, AQAP is more loyal to the central al Qaeda leadership than almost any other part of the sprawling global jihadi network. With the leadership under intense pressure, including from U.S. drone attacks in Pakistan's tribal areas bordering Afghanistan, AQAP has picked up some of the slack in seeking to launch attacks overseas. AQAP claimed responsibility for an attempt on Christmas Day in 2009 to bomb a U.S.-bound passenger plane, and said it provided the explosive device used in the failed attack. In August 2009, an AQAP suicide bomber tried to kill Saudi Arabia's Prince Mohammed bin Nayef. The group also claimed responsibility for a foiled plot to send two air freight packages containing bombs to the United States in October 2010. Western intelligence officials believe the group continues to look for ways to get around aviation security - though its failure to strike outside Yemen might intensify its determination to attack western targets inside Yemen. "They are a small group, but they are deadly, with the capability to take action," said one official. Wuhayshi, according to Johnsen, was one of many al Qaeda members who ended up in Iran after 2001 - the majority fled to Pakistan. After being returned to Yemen in a prisoner exchange with Iran in 2003, he spent most of the next three years in jail before escaping in February 2006. He became leader of al Qaeda in Yemen in 2007, and then head of AQAP in 2009 when al Qaeda's Yemeni and Saudi wings merged. In contrast to al Qaeda in Iraq, which alienated large parts of the local population through its use of widespread violence, AQAP under Wuhayshi has focused on winning over local Yemeni tribes. Its leadership ranks are also dominated by locals from the region. For years Wuhayshi was overlooked as U.S. attention focused on the American-Yemeni preacher Anwar al Awlaki, killed in a U.S. drone strike in 2011. In a eulogy to bin Laden, posted on Islamist militant websites in 2011, Wuhayshi promised that what would come next would be "greater and worse." You have to fight one generation after the other, until your life is ruined, your days are disturbed and you face disgrace. The fight between us and you was not led by Osama alone," he said. Reporting by Myra MacDonald; Editing by Will Waterman