Gulf states hosting U.S. military bases were on high alert Sunday amid fears of regional escalation following American airstrikes on Iran.

U.S. forces "obliterated" Iran's main nuclear sites with massive bunker-busting bombs in the early hours of Sunday in the region, President Donald Trump claimed, warning Tehran it would face more devastating attacks if it does not agree to peace.

Saudi Arabia, the world's largest oil exporter, was on a high security alert after the U.S. strikes, two sources with knowledge of the matter told Reuters on Sunday, while Bahrain urged drivers to avoid main roads and Kuwait set up shelters in a ministry complex.

Tehran has previously warned that if it was attacked by the United States, it could target American assets in the region, including U.S. military bases.

Bahrain is home to the headquarters of the U.S. Navy's 5th Fleet and there are U.S. bases in Saudi Arabia and Kuwait, as well as in neighbouring Qatar and the United Arab Emirates.