Hillary Clinton has called for increased US military and political intervention in north Africa, and warned of a long, difficult but necessary struggle against a "spreading jihadist threat" in the region.

The US secretary of state singled out the French-led intervention against armed Islamists in Mali as the most urgent crisis, but said that al-Qaida in the region, newly armed and invigorated by the fallout of the Arab revolutions, also threatens important allies such as oil-rich Nigeria, as well as the fledgling government in Libya.