Washington (CNN) Two U.S. Navy warships moved into new positions in the Red Sea late Monday to be ready to evacuate Americans from the US embassy in Yemen if an order comes to do so, CNN has learned.

So far, there has been no decision to evacuate the embassy. The USS Iwo Jima and the USS Fort McHenry were moved "because they will be in the best position if asked," by the State Department to evacuate the embassy, a U.S. official with direct knowledge of the planning tells CNN. So far there has been decision to evacuate the embassy, and no request from the State Department for military assistance.

If an evacuation is ordered, the first option would be to have embassy personnel drive to the commercial airport in Sanaa and fly out, the official said. But in the wake of an embassy car being fired Tuesday, the safety of the roads in the capital is now being constantly evaluated, the official said. If embassy workers did drive to the airport it is likely some sort of air cover would be provided, under the current plan.

Other detailed military planning for various options has been finalized, the official said. Those options would be used if a request for military assistance were made.

If helicopters and V-22 aircraft from the ships are sent to Sanaa, it would be a complex operation that could last for several days to fully evacuate "several hundred Americans" from the embassy, the official cautioned. "Nobody should think this would be easy."

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