Iran-aligned Houthis seized control of Yemen’s port city of Mocha on Thursday and advanced down the Red Sea coast to strategic islands, military sources said, hours after President Donald Trump said he expected the Iran war to end after the U.S. midterm elections.

Yemeni government military sources said the Houthis had gained further leverage over the Bab el-Mandeb Strait, the southern outlet of the Red Sea and one of the world’s most important shipping routes, and had reached the islands of Hanish.

If the Houthis were to gain control of the waterway on the opposite side of the Arabian Peninsula from the Strait of Hormuz, it could give their backer Iran a critical advantage in the war with the United States, reducing supplies through a second major transit corridor and sending oil prices surging.

It could also make it harder for Trump to find an exit from a war that has hurt his Republican Party’s electoral prospects ahead of the November midterms.

Yemen’s Houthi-run humanitarian operations coordination centre said in a statement that Red Sea navigation is safe for all shipping companies except for Saudi vessels.

Saudi Arabia, the world’s largest oil exporter, has relied on the Red Sea route since the Iran conflict effectively closed Hormuz, through which a fifth of global oil used to flow.

Yemeni government forces and their allies are relocating south along the Red Sea coast to Dhubab on Bab el-Mandeb Strait, across from Perim Island, government military sources said. Control of Dhubab and the island is key to gaining hold of the strait, they said.

U.N. Special Envoy for Yemen Hans Grundberg told a U.N. Security Council meeting on Thursday that the international community must act to address “a new and more dangerous phase” in the Yemen war.

The Houthis’ gaining control of Mocha gave them “a direct presence on the approaches to one of the world’s most vital straits,” raising serious concerns about freedom of navigation, he said.

Yemeni government, Iranian and regional sources told Reuters the Houthi advance down the coast this week came with direct guidance from Iran’s Revolutionary Guard Corps.

Houthi spokesperson Mohammed Abdulsalam said, without elaborating, that the group’s operations were defensive and would stop once attacks on Yemen stopped.

Oil Prices Jump

Brent crude prices jumped as much as 4% on Thursday above $105 a barrel on concern over disruption to supply routes.

After joining the war with an attack on Israel in March, the Houthis declared a naval blockade against Saudi Arabia in July and escalated attacks this month.

Tensions in the region remained high, with Saudi civil defence authorities issuing emergency alerts in the southwestern city of Khamis Mushait for the fourth time in 24 hours, as the Houthis attacked.

Pakistan has delivered a Saudi warning to Iran to rein in the Houthis to try to prevent the crisis from spiralling, Saudi, Pakistani and Iranian sources said. A senior Iranian official said Tehran’s response was: “Iran does not control the Houthis”.

The fighting comes during the biggest declared wave of U.S.-Iran tit-for-tat attacks on Gulf shipping since the war began in late February.

The U.S. Treasury Department on Thursday announced new sanctions against firms and individuals aiding Hezbollah and other Iranian proxies as part of “Operation Economic Outcast,” which aims to cut off Tehran’s war funding.

Trump Sees War Ending After Midterms

The war and subsequent increase in fuel prices have helped drive Trump’s popularity to record lows, according to polls. He said Iran was trying to influence the midterm elections, which will determine whether his Republican Party retains control of Congress.

“I think war is going to end immediately after the election because they can’t hold out any longer. They’re desperate to try and affect the election,” Trump told reporters on Wednesday.

Trump has previously set other deadlines for the war to end.

In recent weeks Washington had cited increasing success guiding tankers through the Strait of Hormuz, which carried about a fifth of global oil supplies before the war.

But a resumption of fighting this month appears to have set back any such gradual reopening. Just seven vessels transited the strait on Wednesday, half the 10-day average, preliminary ship-tracking data showed.

Iranian state media said on Thursday the Revolutionary Guards Navy had struck a U.S. unmanned vessel at the entrance to Hormuz.

(Reporting by Elwely Elwelly, Jana Choukeir and Nayera Abdallah in Dubai and Enas Alashray in Cairo, and Idrees Ali, Simon Lewis, Steve Holland and David Brunnstrom in Washington; Writing by Lincoln Feast, Alexandra Hudson and Hugh Lawson; Editing by Michael Perry, Sharon Singleton, Timothy Heritage and Cynthia Osterman)