Attacks on tankers in the Red Sea and US bases in the Gulf raised fears that the Middle East conflict could intensify.
Two Saudi ships were struck by Houthi militants, after the Iran-backed group warned it would blockade the Bab el-Mandeb Strait, through which about 10% of global trade passes.
Washington has reportedly moved more troops and ordnance to the Gulf as President Donald Trump considers stepping up hostilities in the wake of Iranian attacks that killed three US soldiers.
The accuracy and sophistication of Iranian strikes on CIA facilities raised questions about Russian involvement, Reuters reported. The fighting and pressure on shipping pushed Brent crude prices above $98 for the first time since early June.