U.S. forces struck Iranian rocket launchers on the Strait of Hormuz in their first military action in a month on Sunday, breaking a lull in fighting during an intermittent war that has lasted more than six months. Iran swiftly vowed to retaliate for what it called a deadly attack.

Forces with the Revolutionary Guard Corps were observed preparing to launch rockets with sea mines into the strait, according to Tim Hawkins, a spokesperson for the U.S. Central Command. The U.S. military last week completed clearing sea mines from the strait’s international shipping routes.

Semiofficial news outlets in Iran reported sounds of explosions near Larak island on the strait. The Guard in a statement carried by Iran’s state broadcaster noted “the martyrdom and injury of several of our fighters and compatriots.”

Later, Iranian state television showed what it said were ballistic missiles being fired by Iran at U.S. bases in Jordan in response to the American strikes. Jordan’s armed forces said they intercepted eight missiles that penetrated the country’s airspace early Monday.

A return to open conflict would be dangerous for the region, where Iran has targeted U.S. military bases and infrastructure in Gulf countries since the war began on Feb. 28.

The last time the U.S. military confirmed targeting Iran was on July 29, when it announced a “heavy wave of strikes” on dozens of Revolutionary Guard targets including coastal surveillance and defense sites. On Aug. 1, President Donald Trump said he would order the military to hold off on new strikes at the urging of Gulf allies Qatar, Saudi Arabia and the United Arab Emirates.

The US had turned to economic pressure
The attack comes just days after the Trump administration said it would turn its focus to increasing economic pressure — rather than military action — to try to end its war with Iran. The shifting strategy centers on threats to punish any country or entity that continues to conduct business with Tehran.