But US aid officials say assurances must be given that the insurgents will not interfere with its distribution.

The US considers al-Shabab a terrorist group and last year stopped aid to the large area of Somalia it controls.

The UN has declared a famine in two areas of southern Somalia as the region experiences the worst drought in more than half a century.

Al-Shabab, an al-Qaeda-affiliated group which controls large swathes of south and central Somalia, had imposed a ban on foreign aid agencies in its territories in 2009, but has recently allowed limited access.

The deputy administrator of the US Agency for International Development, Donald Steinberg, said the aid must not benefit al-Shabab.

"What we need is assurances from the World Food Programme and from other agencies, the United Nations or other agencies, both public and in the non-governmental sector, who are willing to go into Somalia who will tell us affirmatively that they are not being taxed by al-Shabab, they are not being subjected to bribes from al-Shabab, that they can operate unfettered," said Mr Steinberg.

He said the goal was to save lives, "not to play a game of 'gotcha' with a UN agency or any other group that is brave enough to go in and provide that assistance".