U.S. officials said Monday the United States has taken the first step in its planned expanded fight against Islamic State militants, going to the aid of Iraqi security forces near Baghdad who were being attacked by enemy fighters.

The U.S. Central Command said it conducted a strike Monday in support of the Iraqi forces southwest of Baghdad. There was also an airstrike Sunday near Sinjar in northern Iraq.

The strike southwest of Baghdad represents the newly broadened mission authorized by President Barack Obama to go on the offensive against the Islamic State group wherever it is. Previous U.S. airstrikes in Iraq were conducted to protect U.S. interests and personnel, assist Iraqi refugees and secure critical infrastructure. Monday's strike was in direct support of Iraqi forces fighting the militants, hitting fighters who were firing on them.

U.S. officials said the Iraqi forces requested assistance when they came under fire from militants. Those officials spoke on condition of anonymity because they were not authorized to discuss the mission publicly by name.

Central Command said the Sinjar strike destroyed six vehicles belonging to Islamic State militants. (Yonhap)