Airstrikes against the Islamic State group have cost U.S. taxpayers a whopping US$5.5 billion, around US$11.2 million per day, a US$2 million increase since June, according to the latest Defense Department data.

The latest figures also revealed an escalation of airstrikes on the Islamic State group in Syria and Iraq. In November and December alone, the U.S. Air Force dropped more than 3,100 bombs on alleged Islamic State group targets.

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Many of these airstrikes have been run in tandem with ground offensives carried out by local forces to reclaim territory from the extremist group in Iraq and Syria.

Meanwhile, the United States and its allies carried out two dozen strikes against Islamic State extremists in Iraq and Syria Tuesday, the military coalition leading the operations said in a statement.

Sixteen strikes in Iraq were concentrated in Mosul, Ramadi and Kisik, where they hit four of the militant group's tactical units and destroyed four of its bunkers, among other damage, the coalition said in the statement, released Wednesday.

Since June 2014, the Islamic State group has conquered large swaths of territory in Syria and Iraq, killing thousands of soldiers, Shiite Muslims and other religious minorities.

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