"Frankly I would like to see faster progress," he said. "[US support] is not an open-ended commitment".
His arrival in Iraq came hours after a suicide bomber killed at least 12 people in Baghdad; two British soldiers died in the Maysaan province; and a day after one of the deadliest 24 hours in the Iraqi capital.
Yesterday reports claimed that nearly 200 people were killed and a further 250 wounded following a number of car bombs.
The death toll made it the deadliest spate of attacks since the US security crackdown in the capital several months ago.
Earlier this week Mr Gates said that the consequences of not securing peace in Iraq "will adversely affect the security and prosperity of every nation in the Middle East and the Gulf region".
"We have seen the future promised by the extremists: a dark, joyless existence personified not by piety and virtue, but by the executioner and the suicide bomber," he told US businessmen in Cairo.
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