WASHINGTON, July 2(Reuters) - U.S. military advisors have secretly operated in Somalia since around 2007 and Washington plans to deepen its security assistance to help the country fend off threats by Islamist militant group al Shabaab, U.S. officials said.

The comments are the first detailed public acknowledgement of a U.S. military presence in Somalia dating back since the U.S. administration of George W. Bush and add to other signs of a deepening U.S. commitment to Somalia's government, which the Obama administration recognized last year.