Drone strikes on key Saudi oil installations last Saturday have reduced the flow of the world's oil supplies by about five percent.
The US says it will send hundreds of troops and military hardware to Saudi Arabia and the United Arab Emirates.
But it has described the move as a defensive one.
Drone strikes on key Saudi oil installations last Saturday have reduced the flow of the world's oil supplies by about 5%.
Riyadh said 18 drones and three missiles were fired at Abqaiq, the world's largest oil processing facility, while the Khurais facility was hit by four missiles.
No casualties were reported at either site even though thousands of workers and contractors work and live in the area.
"This is the first step we're taking with regard to responding to these attacks," US Secretary of Defence Mark Esper said in Washington DC on Friday.
The presence of western troops in Saudi Arabia has always been a sensitive issue. Osama bin Laden and his al Qaida group described it as a "Crusader invasion" and used their presence to recruit more followers.
Both Saudi Arabia and the United States have blamed Iran for the drone strikes but so far they have not retaliated militarily.
Iran denies involvement in the attack, which was claimed by Yemen's Houthi movement, a group aligned with Iran and currently fighting a Saudi-led alliance in Yemen's civil war.
US Secretary of State Mike Pompeo called the strikes last week "an act of war".
In Iran on Saturday there were reports on social media that a number of Iranian servers and websites — including those of some petrochemical firms — were under a cyber-attack. There was no immediate official comment, and the websites of the main state oil company NIOC appeared to be functioning normally.