ADEN/DUBAI — Yemen’s Iran-aligned Houthis seized control of the historic port city of Mocha on Thursday, four Yemeni government military sources said, gaining further leverage over the Bab el-Mandeb Strait, one of the world’s most important shipping routes.

The Houthis were launching attacks on the strategic Red Sea islands of Hanish, the government sources told Reuters. Government forces and their allies were relocating south to Dhubab, which sits directly on the strait, across from the island of Perim.

Control of Dhubab and the island is key to gaining hold of the strait, they said.

There has been an escalation in fighting in recent days between the Houthis and Saudi Arabia’s Yemeni allies in the internationally backed government, creating a second theater of war in the Iran conflict that threatens global energy supplies.

In 2014, the Houthis seized the Yemeni capital Sanaa, driving the ​internationally recognized government south towards Aden.