The US army on Wednesday transferred to Iraqi forces a key military base in the western province of Anbar near the border with Jordan and Saudi Arabia, a government official said.

"Today we took control of the Al-Assad air base in Anbar province, one of the most important bases in the country," Hussein al-Assadi, who signed the transfer on behalf of the Iraqi authorities, told AFP.

"Counting Al-Assad, we have received 501 bases and there are only four left (under US control.) These are located in Hilla, Diwaniyah, Basra, and Nasiriyah," he said in reference to four bases south of the capital.

"Al-Assad base was returned to the Iraqi army's (ground) forces but they will be given back to the air force," he said, adding that American forces would leave the base in the "coming days."

The US army could not immediately confirm the transfer, but indicated in a statement that "approximately 8,000 US military and defence department civilian personnel" are still in Iraq.