Matthew Tueller has served as US ambassador to both Yemen and Kuwait, and had been previously posted in Baghdad as a political adviser at the American embassy.

On Sunday, Tueller submitted his diplomatic credentials to Iraqi Foreign Minister Mohammed Ali al-Hakim, who said Baghdad would "guarantee all necessary conditions for the success of his mission".

The US Senate confirmed Tueller's appointment in Iraq in mid-May, a day after the State Department announced it was withdrawing all "non-essential" members from its embassy in Baghdad and consulate in Arbil.

The move came amid escalating tensions between the United States and Iran that have repeatedly seen Iraq -- an ally of both countries -- caught in the middle.

The US withdrew from the landmark 2015 nuclear deal with Iran last year, then reinstated tough sanctions on the Islamic republic.

In April, it designated Iran's Islamic Revolutionary Guard Corps as a "terrorist organisation," prompting Iran to slap US troops across the region with the same designation.

And last month, the US deployed a carrier group and B-52 bombers to the Gulf over unspecified Iranian "threats" and a rocket landed in Baghdad's high-security Green Zone, where the US embassy is based.

It sparked fears of a spillover into Iraq, which relies heavily on Iran for energy and consumer goods and where various Shiite armed groups have close ties to Tehran.