The US military on Sunday struck Iran’s Larak Island, where forces were observed preparing to launch rockets with mines into the Strait of Hormuz, according to a US official, marking the first US strikes in over a month.

US forces struck two Iranian launchers on the island, the official said. Residents reported hearing an explosion near Larak Island on Sunday, according to Iran’s semi-official Fars News Agency.

Larak Island is near the strategic Strait of Hormuz, a key global shipping route that has remained at the center of regional tensions and diplomatic efforts.

US Central Command completed clearing sea mines from the waterway’s international shipping routes last week, the Trump administration has said. President Donald Trump said Tuesday that “Iran has been notified that any ship or boat placing new mines will be immediately and systematically destroyed.”

“U.S. forces are monitoring the area closely and remain prepared to protect the free flow of commerce through this essential waterway,” the US official said.