U.S. Defense Secretary Lloyd Austin spoke with Saudi Crown Prince Mohammed bin Salman on Wednesday and emphasized U.S. commitment to helping Saudi Arabia defend its territory and people, the Pentagon said. Austin and Prince Mohammed discussed regional security, particularly efforts to end the war in Yemen, and "ongoing bilateral efforts to improve Saudi Arabia’s defenses," Pentagon spokesman John Kirby said in a statement. Iran-aligned Houthi rebels, who have controlled most of northern Yemen since 2014, have kept up cross-border attacks on Saudi Arabia and are pressing an offensive to seize Yemen"s gas-rich Marib region. A Saudi-led coalition intervened in Yemen in 2015 after the Houthis ousted a Saudi-backed government from the capital Sanaa. The Houthis say they are fighting a corrupt system and foreign aggression. Austin "noted Saudi Arabia’s recent successes in defeating Houthi attacks on the Kingdom" and thanked the crown prince for working with U.S. special envoy for Yemen Tim Lenderking to end the Yemen war, Kirby said. Last month, Lenderking criticized the Houthis for not engaging seriously in stalled efforts to secure a ceasefire. He also urged the coalition to remove restrictions on all Yemeni ports and airports. More than 100,000 people have been killed in the war, most of them civilians, and millions of Yemenis rely on humanitarian assistance to survive.