Iran has announced that it has seized a US-owned unmanned underwater vessel in the Strait of Hormuz, a strategically vital waterway.

Tensions between Iran and the United States have continued to simmer. Iran has said the strait would be reopened only if the US stops what it calls violations, while Washington has been tightening economic sanctions on Tehran.

In its statement, Iran said the captured craft was unmanned and equipped with advanced technology. Iran also claimed its air defence system shot down a US drone in the same area.

The US military, meanwhile, said one of its underwater drones had lost control. No further details were provided in the reports.