A suicide attack at an Afghan air base where US vice-president Dick Cheney was staying shows that the Taliban and al-Qaeda have penetrated local intelligence agencies, analysts and officials said. The blast early on Tuesday at Bagram air base near Kabul also highlights the increasing sophistication of the extremist outfits as they prepare for a feared spring offensive against Western troops, they said. The day before the explosion Cheney warned President Pervez Musharraf of neighbouring Pakistan to crack down on militants regrouping in Pakistan's tribal areas to mount attacks across the border and further afield. "This shows how much the militants have penetrated the intelligence of the Afghan security forces. It is a most shocking attack," retired Pakistani general turned analyst Talat Masood told AFP.