The cost of the American military campaign against ISIS likely has passed $1 billion.
The Pentagon estimated that the U.S. air operation cost $7.5 million per day when surveillance flights began over Iraq on June 16. That estimate increased to $10 million when bombing began Aug. 8.
That alone would put the estimated cost at $937 million. On the first night of the strikes in Syria, the United States also fired 47 Tomahawk missiles, which cost more than $1 million each, higher for more advanced models.
The Center for Strategic and Budgetary Assessments, a nonprofit research institute, estimated earlier this week that the cost through Sept. 24, almost a week ago, was $780 million to $930 million.
The military said Tuesday that American forces had carried out 11 airstrikes in Syria over two days, striking ISIS vehicles, a tank, artillery, fighting positions and several buildings.
The U.S. has carried out more than 200 airstrikes in Iraq, and the U.S. and Arab allies have carried out more than 60 in Syria, according to the military.
—By Courtney Kube and Erin McClam, NBC News