The United States carried out another round of air strikes Monday against militants from the so-called Islamic States battling Iraqi and Kurdish forces near a major dam in northern Iraq.

The Mosul Dam, just north of the city of the same name, has become a focus of fighting between jihadists and Kurdish forces since the United States launched an air campaign last month.

US Central Command said US jets had continued their bombardment of IS positions on Sunday and Monday.

"The strikes destroyed three ISIL trucks, severely damaged another, destroyed an ISIL armed vehicle, and destroyed a mortar position near the Mosul Dam," the military said in a statement.

"All aircraft exited the strike area safely."

Since US aircraft went into action they have carried out 123 separate strikes, more than half of them in defense of the dam, and have helped Kurdish and Iraqi troops reverse some recent IS gains.

Over the weekend, the US campaign moved south to help Iraqi troops and Shiite militias break the 11-week siege of the town of Amerli, where civilians from the Turkmen minority were in danger.