The Pentagon on Monday denied reports it is building two airfields in northern Syria as part of the battle against the "Islamic State" (ISIS) terrorist group, AFP reports.

Syrian military and security officials have said the United States is expanding an airfield in Rmeilan, in Hasakeh province, and new reports have surfaced of a base near the Kurdish city of Kobani.

"We are not building or operating any air bases in Syria," Pentagon spokesman Captain Jeff Davis told reporters.