Pentagon spokesman Rear Adm. John Kirby says the Mesa Verde has already moved into the Gulf, joining the aircraft carrier USS George H.W. Bush and other U.S. naval ships.
Kirby says the ships' presence will give President Barack Obama "additional options to protect American citizens and interests in Iraq."
The Pentagon says the Mesa Verde carries Osprey tilt-rotor aircraft that can be used for crisis response.
The State Department is reinforcing security at the U.S. Embassy in Baghdad and evacuating some personnel. The militant Islamic State of Iraq and the Levant, or ISIL, has taken over several cities in northern Iraq.
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