President Donald Trump's national security adviser, a longtime hawk on Iran, is visiting the United Arab Emirates amid heightened tensions across the Persian Gulf.

John Bolton tweeted he had arrived in the Emirates for meetings Wednesday "to discuss important and timely regional security matters."

America recently deployed an aircraft carrier and B-52 bombers to the Persian Gulf over a still-unexplained threat it perceives from Tehran. The U.S. also pulled nonessential diplomats out of Iraq and sent hundreds more troops to the region.

Meanwhile, Emirati officials allege four ships off their coast were sabotaged. Yemen's Iranian-backed Houthi rebels have launched drone attacks on Saudi Arabia.

The U.S. pulled out of Iran's nuclear deal with world powers a year ago. Iran now says it too will begin backing away from the accord.