President Barak Obama and the state department have been under pressure to take stronger action against the Islamist terrorist sect for months and formally include it on its terrorist watch list.

Republican senator Scott Brown wrote to secretary of state Hillary Clinton, urging her to take action against the group.

But 20 American experts on Nigerian politics warned that branding Boko Haram as a terrorist organisation would empower the group on an international level and enhance its profile among al-Qaida and other militant groups.