Defense expert Cameron Chell called Iran's military moves a "calculated escalation" as U.S. MQ-9 Reaper drones with strike capabilities were reportedly spotted in the region.

The move came amid heightened US military deployments in West Asia, open threats of force from Washington, and domestic unrest inside Iran following a violent crackdown on protests.

Iran shut down the Strait of Hormuz for a few hours on Tuesday, Iranian state media reported, without making clear whether the waterway, one of the world's most vital oil export routes, had fully reopened.

A U.S.-flagged tanker heading for Bahrain was approached and threatened by Iranian gunboats in the Strait of Hormuz, a British maritime security firm says.

Iran temporarily shut part of the key Strait of Hormuz as tensions with the US continue to mount. Tuesday’s move is the first time the Middle Eastern waterway has been closed since the 1980s, and came as Iran’s ayatollah issued fresh threats against the United States.