Pence's unannounced landing at Ain al-Asad base -- his first visit to Iraq as vice president -- came nearly a year after President Donald Trump made his own surprise trip to the sprawling complex.

Trump drew criticism for the lightning-fast visit, in which he briefly met with troops but did not see any Iraqi officials.

That visit was veiled in such secrecy there was speculation that most Iraqi authorities had not been informed the president was coming.

No schedule has been announced for Pence's visit, and the US embassy in Baghdad told AFP it had no details to share on the trip.

The US has 5,200 troops stationed in Iraqi bases across the country.

Washington led the 2003 invasion of Iraq that toppled then-dictator Saddam Hussein, dismantled its security forces and then attempted to rebuild the country's institutions.

After years of working closely together, ties between the two countries are currently at their "coldest", US and Iraqi officials have told AFP.

Prime Minister Adel Abdel Mahdi, in office for the past year, has yet to visit Washington, and Trump has not met top officials in Baghdad.