Two of the anti-missile batteries deployed following the September attacks on Saudi oil installations "are now leaving," the official said on condition of anonymity.

Tehran and Huthi-backed rebels in Yemen were blamed for the combination rocket and drone attack which left two of state oil giant Aramco's processing facilities -- one in Khurais and another in Abqaiq -- heavily damaged, roughly halving Saudi Arabia's oil production.

Two other batteries had been kept in the region in March following an attack by pro-Iran factions on the Iraqi base of Taji, north of Baghdad. Two Americans and one British soldier were killed in the attack.

"I think everyone knew it was going to be a temporary plus-up at the time, unless things got bad, " the official said.

"Things did not get bad, so they had to go."

The batteries' return will also mark the withdrawal of the 300 US personnel who operate them.

Late last year the Pentagon deployed about 3,000 extra troops, fighter jets and other hardware along with the Patriots in the wake of the attack on oil installations and subsequent rise in tensions in the Gulf.

The US also expanded its naval presence in the region.

The aim was to augment the kingdom's air and missile defense against possible rocket attacks from Iran.

In February Greece said it would deploy some of its own Patriot missiles to Saudi Arabia, in a program arranged by the United States, Britain and France.