Leading article: A promotion that gives no comfort

The man who has taken over from Osama bin Laden as head of al-Qa'ida is said to lack the charisma of the terrorist leader the Americans killed six weeks ago. But few believe that he will be less deadly. Ayman al-Zawahiri, a former ophthalmologist, is credited with being the man who lifted Bin Laden's eyes from the local to the global in the days when the chief complaint of the violent jihadist was that US troops were trampling their infidel boots on the Saudi soil which is home to Islam's holiest places. Zawahiri alerted him to a whole range of Muslim grievances – from Kashmir to Palestine – and set up with him the World Islamic Front for Jihad against Jews and Crusaders. Some say he was also the operational brains behind 9/11.

The West can take some comfort that it has taken so long for al-Qa'ida to announce the succession, despite the fact that Zawahiri was Bin Laden's deputy. The delay may suggest divisions at the top of the terrorist organisation. But al-Qa'ida's new leader is a formidable figure. His declared long-term aim is to topple Muslim regimes which collaborate with America, and what is now going on in Pakistan provides chill evidence of his approach.

The country is clearly divided in its attitude to terrorism. That is clear from Pakistan's recent arrest of five men suspected of having aided the United States in the raid that killed Bin Laden. For it shows the clear need of the Pakistani authorities to appease a significant anti-American constituency within its population.

Last week Zawahiri warned that Bin Laden would continue to terrify the US from beyond the grave. What is happening in Pakistan shows how al-Qa'ida intends to do that. The West needs be shrewd here. Cutting the number of aid projects the US funds in Pakistan by two thirds may play well in America, but Washington has a tightrope to walk. Drifting toward a more contentious or fractured relationship with Pakistan plays into al-Qa'ida's strategic plan and risks allowing nuclear weapons to fall into terrorist hands. The West needs to rebuild its intelligence and military relationship with Pakistan. To jeopardise that risks allowing Zawahiri his first victory.