US Defense Secretary Mark Esper has arrived in Saudi Arabia on an unannounced visit, a few days after the Pentagon said it was strengthening its power in the kingdom amid tensions with Iran, AFP reported.

Esper arrived in Riyadh after a visit to Afghanistan.

The Pentagon announced earlier in October it would deploy additional US troops to Saudi Arabia after Riyadh requested reinforcements because of a drone attack on the Saudi oil refineries that Washington accuses Iran of.

Esper said two fighter squadrons and additional anti-ballistic missile batteries were sent to Saudi Arabia, bringing the total number of troops deployed there since last month to about 3,000.