Somalia's Shebab insurgents on Monday banned the aid agency Islamic Relief, one of the very few groups who were able to work in the war-ravaged region controlled by the Al-Qaeda linked fighters.

The Shebab said it "has officially revoked Islamic Relief's permit to work" in the areas it controls, according to messages posted on its Twitter account, which were authenticated by Shebab officials.

Somalia, ravaged by nearly uninterrupted civil war for the past two decades, is one of the most dangerous places in the world for aid workers and one of the regions that needs them most.

While the hardline gunmen have lost control of a string of towns in recent months to African Union troops and Somali government soldiers, they still control large parts of rural southern and central Somalia.

Last year the Shebab ordered shut a slew of United Nations agencies including the World Food Programme as well as other international aid agencies.

The Shebab said the Islamic Relief group was being banned because it "has repeatedly failed, despite the persistent warnings, to comply with the operational guidelines" established by the insurgents.

"Islamic Relief was also found to be covertly extending the operations of banned organisations, particularly WFP," the Shebab added.

The British-based aid agency has worked in Somalia since 1996, with projects focused on "improving access to water, healthcare and education for pastoral communities and people who have fled their homes due to conflict, floods or drought," according to its website.

Somalia was the Horn of Africa country worst hit by a harsh drought last year that left some 12 million people in dire need of relief aid, with several areas in the country declared famine zones.

Islamic Relief was not immediately available for comment Monday.