Yemen's Houthi rebels seized the strategic islands of Greater Hanish and Lesser Hanish in the southern Red Sea on Monday, according to Yemeni government and Houthi officials. The moves strengthen the Iranian-backed group's control over a critical shipping lane.

The islands lie about 160 kilometers north of the Bab el-Mandeb Strait. Houthi fighters deployed there after hundreds of Saudi-backed government-allied forces withdrew from the archipelago. Officials spoke on condition of anonymity because they lacked authorization to discuss the matter publicly.

This latest advance follows the rebels' seizure last week of the mainland port city of Mokha and the island of Mayun inside the Bab el-Mandeb Strait. Those gains came with minimal resistance from forces of the internationally recognized Yemeni government.

The Bab el-Mandeb Strait serves as a vital alternative route for Saudi crude oil exports amid disruptions in the Strait of Hormuz tied to the Iran conflict. Houthi control over additional islands increases pressure on global energy supplies and shipping costs.

Saudi-backed Yemeni government forces attempted to regroup over the weekend and launched attacks against Houthi positions along the Red Sea coast. The Yemeni military reported advances toward the town of Dhubab north of the strait on Sunday. The government has vowed to reinforce its presence on the coast.

The Houthi expansions heighten risks to international maritime traffic and add volatility to oil markets. The rebels have conducted strikes on Saudi infrastructure and shipping in the Red Sea for more than a month.