At least three rockets hit the Iraqi military air base of Balad, north of Baghdad, where some US contractors are billeted, Iraqi security officials said on Monday.
Three other rockets fell near the base in the attack on Sunday, the sources said.
No casualties or damage have been reported.
No group has claimed responsibility, but armed groups that some Iraqi officials say are backed by Iran have claimed similar incidents in the past.
Source: Asharq Al-Awsat