The United States has ordered two warships and 400 Marines to the waters off Libya, but top U.S. military officials played down the likelihood that the forces would intervene in the country’s growing civil war.

U.S. Defense Secretary Robert Gates said Tuesday he has ordered to the Mediterranean two amphibious assault ships in case they are needed for emergency evacuations or humanitarian relief. The Marines, currently in the U.S., would be deployed to meet the ships, which are scheduled to travel through Egypt’s Suez Canal on Wednesday.

Gates said the U.S. is preparing many “options and contingencies” for President Barack Obama to consider in response to the violence in Libya and general instability in the region. Gates did not rule out establishing a no-fly zone to prevent Libyan leader Moammar Gadhafi from carrying out airstrikes against rebel forces. But he said there is no international consensus for military action against the Libyan regime.

The top U.S. military officer, Admiral Mike Mullen, said a no-fly zone would be an “extraordinarily complex” operation. In separate testimony before a congressional panel Tuesday, General James Mattis said it would be necessary to pre-emptively attack Libyan air-defense installations to ensure they could not shoot down U.S. or NATO planes.

Meanwhile, U.S. Secretary of State Hillary Clinton warned Libya could become a “peaceful democracy” or face “protracted civil war.”

The top U.S. diplomat Tuesday repeated calls for Libyan leader Moammar Gadhafi to step down. She told lawmakers in Washington that “the stakes are high,” saying the right combination of U.S. diplomatic, development and defense efforts will be crucial.

Clinton said Washington will continue considering all options on Libya as long as the government continues to “turn its guns on its own people.” She also said the Obama administration may seek the prosecution of Mr. Gadhafi for the 1988 Lockerbie bombing in response to lawmakers’ requests.

European foreign ministers meeting with Clinton Monday expressed skepticism that a no-fly zone for Libya could be effective and concern over how it would be viewed by other Arab nations.

Turkish Prime Minister Recep Tayyip Erdogan Tuesday called potential NATO intervention in Libya “unthinkable.”