"Terrorist sanctuary in the tribal areas of Pakistan will continue to challenge Afghan security," nominated Assistant Secretary of Defence for Special Operations and Low Intensity Conflict Michael D Lumpkin said yesterday.

The Pentagon official also said the US must remain cautious in Afghanistan as the allied forces begin to withdraw in 2014. "Both unilateral and partnered direct actions are an essential and highly effective element of our strategy to defeat al-Qaeda and those that enable it in Afghanistan, particularly in northeastern parts of the country," he said.