The US will put no "boots on the ground" in Libya, Defense Secretary Robert Gates has reaffirmed in Congress, after reports emerged that President Obama has authorized covert CIA aid to rebels. Admiral Mike Mullen, the Chairman of the Joint Chiefs of Staff, said the operation had already degraded Libyan leader Muammar Gaddafi's forces by up to 25%. The remarks came as rebels retreated from towns on Libya's eastern coast. The BBC's World Affairs Editor John Simpson is in Tripoli.