The Pentagon said on Sunday that it targeted an Iran-linked militant group in western Iraq and eastern Syria in response to a barrage of rockets that killed a US civilian contractor two days earlier.

"These attacks have once again proved America's false claims in fighting Daesh... as the United States has targeted the positions of forces that over the years have inflicted heavy blows to Daesh terrorists," Iran's government spokesman Abbas Mousavi said, referring to IS.

"With these attacks, America has shown its firm support for terrorism and its neglect for the independence and sovereignty of countries and it must accept consequences for its illegal act," he said in a statement.

The spokesman said the presence of foreign forces in the region was the cause of insecurity and tensions.

"America must put an end to its occupying presence," said Mousavi.

US-Iran tensions have soared since Washington pulled out of a landmark nuclear agreement with Tehran last year and began reimposing crippling sanctions.