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The Pentagon is sending another ship to the Persian Gulf to give President Barack Obama "additional options to protect American citizens and interests in Iraq," an official said Monday.

The amphibious transport dock ship USS Mesa Verde — which carries Osprey combat helicopters — will join other U.S. naval ships already in the gulf, including the aircraft carrier USS George H.W. Bush.

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According to one senior defense official, “If the President orders airstrikes, we have plenty of firepower in the Gulf.”

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The move comes as the turmoil in Iraq deepens. The Shiite-led government has lost a huge swath of northern land to Sunni militants, who captured the key city of Tal Afar before dawn on Monday.

The presence of the USS Mesa Verde "provides the commander-in-chief additional options to protect American citizens and interests in Iraq, should he choose to use them," Pentagon press secretary Rear Adm. John Kirby said.

The Defense Department said the ship was in the region on a routine deployment and is "capable of conducting a variety of quick reaction and crisis response operations."

Along with the Bush and the Mesa Verde, the U.S. has four guided missile destroyers in the Gulf: The USS Arleigh Burke, Truxtun, O'Kane and Phillipine Sea.

— Jim Miklaszewski and Courtney Kube