The U.S. military attacked Iranian rocket launchers positioned in the Strait of Hormuz, marking its first offensive operation in a month, a U.S. official told The Associated Press on Sunday.

Explosions were heard near Larak Island, which lies in the waterway, Iranian media outlets reported.

Iranian forces had been preparing to launch rockets carrying mines into the strait, the unnamed U.S. official said. The waterway, a vital trade route, has emerged as a major flash point in the war.

Last week, the U.S. completed an operation to clear mines from strait’s shipping lanes. Following the operation, President Donald Trump warned Iran that “any ship or boat placing new mines will be immediately and systematically destroyed.”

In response to the new offensive, the Islamic Revolutionary Guard Corps said in a statement that the U.S. attack “will be answered by the sons of Iran and will result in the punishment of the aggressor,” Axios reported.

When reached for comment, a Pentagon spokesperson referred The Independent to U.S. Central Command, which oversees U.S. operations in the Middle East.

The war, which began in February when the U.S. and Israel attacked Iran, had largely settled into a stalemate in recent weeks with no clear end in sight.

The strait, which carried about 20 percent of the world’s oil before the conflict, has remained a central obstacle. The U.S. insists it must remain open to unrestricted shipping, while Iran says it has the right to manage traffic through the waterway.

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