Bases in Iraq and Syria hosting the US-led military coalition against the self-proclaimed Islamic State (IS) terrorist group were targeted by several missile attacks on July 25 and 26, security sources said.
One source in Iraq said four missiles fell near the Ain al-Assad base in Anbar province, while another source said it was an attack by a drone and three missiles.
Initial reports indicate the shells landed outside the base without causing any injuries or damage, a US official said.
The UK-based Syrian Observatory for Human Rights (SOHR) said at least one missile had fallen near a coalition base at the Conoco gas field in the eastern Syrian province of Deir Ezzor. Explosions were heard in the area, but there were no reports of casualties.
No force has yet claimed responsibility for the attacks.
Over the past three months, as regional tensions have risen due to the conflict between Israel and the Hamas Islamist movement in the Gaza Strip, US bases in the Middle East, mainly in Iraq and Syria, have been attacked at least 175 times.
The latest attack comes on the heels of a meeting this week between Iraqi and US officials in Washington on the future of the international coalition against IS. Iran-backed groups in Iraq have called for the US-led coalition to withdraw.
The US military currently maintains about 2,500 troops stationed in Iraq and 900 troops stationed in Syria.