Britain and Pakistan have agreed to work harder together to fight Islamist militancy, following criticism by Prime Minister David Cameron of Pakistan's efforts in countering extremism.

Cameron met Pakistani President Asif Ali Zardari at Chequers on Friday.

"Both leaders appreciated the close co-operation that already exists between respective police forces and other security agencies," a joint statement from the leaders said.

"The two leaders agreed that such co-operation needs to and will intensify."