A blockade would stop piracy and the flow of arms reaching insurgent groups fighting the transitional government, said Ramtane Lamamra, AU commissioner for peace and security.
Mr. Lamamra also repeated a call for international troop numbers to be increased from under 8,000 to 20,000.
Somalia's fragile government is battling an Islamist insurgency. The al-Shabab militia - which now controls much of southern and central Somalia, including parts of the capital, Mogadishu - is linked to al-Qaeda. However, the government, backed by AU peacekeepers, has recently gained some ground.