Somalia's most prominent rebel group, al-Shabab, has banned the United Nations World Food Program and ordered the agency to leave the impoverished country.

In a statement, the al-Qaida-linked rebels said starting Sunday, WFP operations would be terminated.  It warned any local contractors working for the agency to quit or be found guilty of serving as an accomplice.

Al-Shabab said the WFP was having a negative impact on local farmers and accused the group of giving out expired food.  It also charged the agency with having a political agenda.

The WFP had already suspended operations in southern Somalia in January, citing "unacceptable" demands from armed groups and attacks on its relief work.

Al-Shabab controls much of southern and central Somalia, where fighting between rebels and government troops has exacerbated one of the world's worst humanitarian crises.  The U.N. says half of Somalia's population is in need of aid.

Somalia has endured nearly two decades of unrest and instability since the fall of the last stable government in 1991.  

Close to 1.5 million Somalis are displaced inside the country, and 560,000 are registered as refugees in neighboring countries.

Some information for this report provided by AP, AFP and Reuters.