CAIRO — A week of Houthi attacks and territorial gains in Yemen is intensifying pressure on Saudi Arabia’s oil exports, threatening shipping through one of the world’s most important maritime passages and worsening an already severe humanitarian crisis. The Iran-backed group seized the Red Sea port of Mokha and several nearby islands before moving toward the Bab el-Mandeb strait, a narrow waterway through which roughly 12% of global trade passes during peacetime. Houthi forces are also within about 20 miles of Djibouti, where the United States and other countries maintain military bases. The offensive is the Houthis’ largest territorial expansion in years and has effectively reignited Yemen’s civil war, which began when the group captured the capital, Sanaa, and large parts of the north in 2014. Saudi Arabia intervened the following year in support of Yemen’s internationally recognized government. A ceasefire in 2022 brought a period of relative calm, but it did not resolve the conflict. Fighting has recently intensified around Marib, an oil-rich central province and military stronghold for Saudi-backed forces. The Houthis also threaten Taiz, a western city that has remained a major front line. Their next apparent objective may be Yemen’s oil-producing east, though the Saudi-backed government and rival armed factions remain in their path. The group has launched attacks against Saudi oil facilities and tankers. A separate strike on Saudi Arabia’s east-west oil pipeline, which Riyadh blamed on Iran-backed militias in Iraq, has added to concerns about disruptions to the kingdom’s energy exports and sent tremors through global markets. The Houthis say their attacks are aimed at Saudi-linked shipping and demand an end to the long-running blockade on territory under their control. Mohammed al-Bukhaiti, a member of the group’s political bureau, said Saudi Arabia had blocked shipping to and from Yemen and imposed an “unjust blockade.” Shipping traffic through Bab el-Mandeb initially fell from about 35 daily transits to 25 after the Houthi advance, according to the maritime data firm Windward. Traffic later rebounded, reaching 45 transits on a recent Sunday. The recovery could prove temporary if the Houthis broaden their definition of what constitutes a Saudi-linked vessel. Valentin d’Hauthuille, a Middle East analyst with conflict monitor ACLED, said the Houthis were currently concentrating on Saudi-linked ships but could expand their targeting criteria to increase pressure on Saudi Arabia and the global economy. During an earlier campaign tied to the Gaza war, the group attacked Red Sea vessels with no clear connection to the conflict. The United States has maintained contact with Saudi officials but has shown no indication that it plans to intervene militarily. Washington previously carried out strikes against Houthi targets under both the Biden and Trump administrations. The Houthis, meanwhile, appear to be trying to avoid provoking direct U.S. involvement. Diplomatic efforts are underway. Oman hosted a meeting between U.S. and Houthi representatives last weekend, according to a Houthi official and another person familiar with the discussions. Saudi Crown Prince Mohammed bin Salman recently visited Egypt, which has played a mediating role, while Turkey said it was consulting with Iran and the United Arab Emirates about lowering regional tensions. A settlement appears difficult without progress in the broader confrontation involving Iran. Tehran is seeking relief from a U.S. blockade and sanctions, while Washington is pressing for the reopening of the Strait of Hormuz and limits on Iran’s nuclear program. A preliminary agreement collapsed over the summer, and neither side has signaled a willingness to compromise. The escalation is also testing a new defense agreement involving Saudi Arabia, NATO member Turkey and nuclear-armed Pakistan. Officials in Turkey and Pakistan said they had not received a request from Riyadh for military assistance. For civilians in Yemen, the renewed fighting has brought immediate costs. The United Nations humanitarian office said eight civilians had been killed and 32 wounded in the latest violence, while about 125,000 people had fled their homes. Yemen’s Saudi-backed Health Ministry reported that Houthi attacks had killed about 150 civilians since Sept. 3, though battlefield casualty figures are difficult to independently verify. Saudi authorities said debris from an intercepted Houthi drone killed one person and wounded two others in the kingdom on Thursday. Yemen was already the Arab world’s poorest country before the war, and years of fighting, hunger and blockade have left millions dependent on aid. The Houthis’ detention of U.N. and aid workers has further restricted assistance in areas they control. The United Nations says its humanitarian appeal for Yemen is only 20% funded and warns that millions could lose access to food, health care, clean water and protection services. “The needs are extremely high right now,” said Sara Ahmed, a supervisor with Doctors Without Borders in Mokha. She said medical workers were struggling to keep essential services operating while hearing airstrikes nearby. Mahida Ahmed, who fled Mokha with her children, is sheltering in a displacement camp in Aden. She left without belongings, while her husband remains trapped in Mokha. “This war has been completely devastating for us,” she said.