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U.S Defense Secretary Carter arrives in Iraq

  • This undated photo provided by the U.S. Navy shows Chief Petty Officer Jason C. Finan. Finan, whose hometown was listed by the Pentagon as Anaheim, Calif., was assigned to Explosive Ordnance Disposal Mobile Unit Three. He was killed in Iraq Thursday, Oct. 20, 2016. He died of wounds sustained in a roadside bomb attack north of Mosul. Finan was part of a U.S. team advising and assisting Iraqi Kurd fighters known as peshmerga. (U.S. Navy via AP)

    This undated photo provided by the U.S. Navy shows Chief Petty Officer Jason C. Finan. Finan, whose hometown was listed by the Pentagon as Anaheim, Calif., was assigned to Explosive Ordnance Disposal Mobile Unit Three. He was killed in Iraq Thursday, Oct. 20, 2016. He died of wounds sustained in a roadside bomb attack north of Mosul. Finan was part of a U.S. team advising and assisting Iraqi Kurd fighters known as peshmerga. (U.S. Navy via AP)  (The Associated Press)

  • U.S. Defense Secretary Ash Carter arrives in Baghdad, Iraq to meet with his commanders and assess the progress in the opening days of the operation to retake the city of Mosul from Islamic State militants, on Saturday, Oct. 22, 2016. His visit comes two days after a U.S. service member was killed outside Mosul, underscoring the risk that American troops are taking as they advise Iraqi forces in the fight. (AP Photo/Lolita Baldor)

    U.S. Defense Secretary Ash Carter arrives in Baghdad, Iraq to meet with his commanders and assess the progress in the opening days of the operation to retake the city of Mosul from Islamic State militants, on Saturday, Oct. 22, 2016. His visit comes two days after a U.S. service member was killed outside Mosul, underscoring the risk that American troops are taking as they advise Iraqi forces in the fight. (AP Photo/Lolita Baldor)  (The Associated Press)

  • Iraqi troops guards a checkpoint near the village of Awsaja, Iraq, as smoke from fires lit by Islamic State militants at oil wells and a sulfur plant fills the air on Saturday, Oct. 22, 2016.   U.S. military officials say that a fire at the sulfur plant in northern Iraq is creating a potential breathing hazard for American forces and other troops at a logistical base south of Mosul.  (AP Photo/Adam Schreck)

    Iraqi troops guards a checkpoint near the village of Awsaja, Iraq, as smoke from fires lit by Islamic State militants at oil wells and a sulfur plant fills the air on Saturday, Oct. 22, 2016. U.S. military officials say that a fire at the sulfur plant in northern Iraq is creating a potential breathing hazard for American forces and other troops at a logistical base south of Mosul. (AP Photo/Adam Schreck)  (The Associated Press)

U.S. Defense Secretary Ash Carter arrived in Iraq Saturday to meet with his commanders and assess progress in the opening days of the operation to retake the northern city of Mosul from Islamic State militants.

His unannounced visit comes two days after a U.S. service member was killed outside Mosul, underscoring the risk to American troops as they advise Iraqi forces. And it comes on the heels of Carter announcing there "is an agreement in principle" for Turkey to help in the Mosul battle, and that friction between Turkey and Iraq can be worked out.

This is Carter's third trip to Iraq this year, and he has overseen the steady increase in the number of U.S. forces deployed and the growth of America's effort to train and advise Iraqi troops.