Two Saudi fighter pilots were missing after Iran-backed Yemen Houthis said they shot down a Saudi fighter jet, a potential escalation in their five-year war.

Saudi coalition spokesman Colonel Turki Al-Maliki said the pilots ejected before their Tornado jet crashed on Saturday in Yemen while under attack by Houthis, according to the official Saudi Press Agency. The Houthis said they had shot down the warplane in northwestern Al Jawf province, where they are fighting Saudi-backed government forces, according to the Houthi-owned Al-Masirah TV.

The missile that downed the fighter jet is a part of a new defense system made locally and that was its first test, Al-Masirah TV reported. The Houthis said coalition warplanes launched several strikes on the area where the plane went down, and the United Nations reported 31 civilians were killed.

The Saudi-led coalition has been battling the Houthis in an effort to reinstate ousted President Abd Rabbuh Mansur Hadi. The war has produced the worst humanitarian crisis in the world, with tens of thousands of people dead or injured and millions displaced, according to the UN.

Mohammed Al-Hadhrami, the foreign minister of Yemen’s internationally recognized government, told Bloomberg TV that the U.S. administration’s “maximum pressure” campaign on Iran has produced “good results.”

“Keep the pressure on Iran and you will see peace in Yemen,” he said in an interview in Munich on Friday.

Last week, the U.S. Navy seized a boat allegedly carrying Iranian weapons to the Houthis , including three surface-to-air missiles and 150 antitank missiles. Iran has denied providing weapons to the Houthis, who have taken credit for attacks on neighboring Saudi Arabia.

-Bloomberg