US Secretary of Defence Mark Esper arrived Monday in Saudi Arabia, state television said, days after the Pentagon said it was bolstering its forces in the kingdom amid tensions with Iran.
Al-Ekhbariyah television gave no details on the previously unannounced visit, which comes after Esper visited Afghanistan.
On October 11, the Pentagon said it was deploying new US troops to Saudi Arabia after Riyadh asked for reinforcements following a mid-September drone and missile attack on Saudi oil plants, which Washington blames on Iran.
Esper said that two fighter squadrons and additional missile defence batteries were being sent to Saudi Arabia, bringing to about 3,000 the total number of troops deployed there since last month.
The September 14 attack knocked out two major processing facilities of state oil giant Aramco in Khurais and Abqaiq, roughly halving Saudi Arabia's oil production.
Washington condemned the attacks as a "act of war" but neither the Saudis nor the United States have overtly retaliated.
Tensions have soared in the Gulf in recent months with a series of attacks on oil infrastructure and tankers, raising fears of a war between the arch-rivals.
Iran has denied any involvement.