The United States and Iran exchanged fire for the first time in a month, marking a fresh escalation in a conflict that had seen its last major U.S. strikes in late July. According to the Guardian, missiles and drones were fired at Iranian rocket launchers on an island in the strait of Hormuz, while Iran targeted U.S. military bases in Jordan and the United Arab Emirates in response.

President Donald Trump threatened further action on Monday, the Guardian reported, as Washington pressed its campaign to weaken Tehran’s grip over shipping through the strategic waterway.

Washington said it acted after observing that Iran was planning to deploy fresh mines in the strait of Hormuz, according to the Guardian. The U.S. claimed that Iranian control over the waterway had been loosened by repeated American attacks on Iranian missile launchers and radars.

The strait of Hormuz sits at the center of the confrontation. Before the war, the Guardian reported, the waterway accounted for a fifth of the world’s seaborne energy supply, making it one of the most important chokepoints for global energy trade.

The latest exchange breaks a relative lull in direct hostilities. CNBC noted that the last major U.S. strikes on Iran were carried out in late July, meaning the two sides had not directly traded fire for roughly a month before the renewed flare-up.

The strikes on U.S. bases in Jordan and the UAE widen the geographic footprint of the conflict, drawing in locations across the region as both sides continue to contest control of the strait and the shipping lanes that run through it.