Iran announced Tuesday the temporary closure of the Strait of Hormuz for live-fire military drills, in a rare show of force as negotiators held indirect talks with the United States in Geneva over its disputed nuclear program.

It was the first time Iran had announced the closure of the key international waterway, through which 20% of the world’s oil passes, since the U.S. began threatening Iran and rushing military assets to the region. It marks a further escalation in a weekslong standoff that could ignite another war in the Middle East.

As the talks began, Iran’s state media announced that it had fired live missiles toward the Strait and would close it for several hours for "safety and maritime concerns."

The semiofficial Tasnim news agency, which is close to the paramilitary Revolutionary Guard, said missiles launched inside Iran and along its coast had struck their targets in the Strait.

Iranian state TV later said the talks had wrapped up after almost three hours.