The meeting in Riyadh, where Esper arrived late Monday after an unannounced visit to Afghanistan, also took in defence issues and the current situation in the region, the official SPA news agency said.

The agency later added that Esper had met powerful Crown Prince Mohammed bin Salman, who is also defence minister.

The two discussed "military and defence cooperation", it said.

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 has 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 US troops deployed to the kingdom since last month.

The September 14 attack knocked out two major facilities of state oil giant Aramco in Abqaiq and Khurais, roughly halving Saudi Arabia's oil production.

Washington condemned the attacks as an "act of war" but neither Saudi Arabia 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 war. Iran has denied any involvement.