Speaking ahead of a NATO defense ministers' meeting in Lithuania, de Hoop Scheffer said Afghanistan is the "front-line in the fight against terrorism, and what is happening in the Hindu Kush matters." "If terrorism is not dealt with in Afghanistan, the consequences will be felt not just in Afghanistan and the region, but also in London, Brussels and Amsterdam," he told the BBC.

His warning came as US Secretary of State Condoleezza Rice and UK Foreign Secretary David Miliband flew from London to Afghanistan on an unannounced visit.

On Tuesday, the International Institute for Strategic Studies (IISS) in London, echoed other reports in saying that Afghanistan faced becoming a "failed state" if operations by Nato were unsuccessful.

The NATO chief said he would be spelling out to defense ministers that reluctant member nations must do more to train and equip the Afghan army.

The challenges that remain include the adequate training and equipping of the Afghan national army, but Nato's mission in the country, the first out-of-area, was one of necessity, not choice, he insisted.

On Wednesday, Rice discussed with Miliband and Britain's Prime Minister Gordon Brown ways to get Nato members to share the burden of the fighting in the country's south.

The two allies currently supply more than half of NATO's 41,000 in Afghanistan, with the US deploying more than 15,000 and the UK nearly 8,000.