Limits to the progress of the Saudi Arabia-led war on Yemen’s Shiite rebels were on full display this weekend.

The Saudi military said on Saturday it shot down a Scud missile fired into the kingdom from Yemen. Saudi troops also repelled an attack on the border, killing dozens of gunmen. Four Saudi soldiers lost their lives in the battle, state-run media reported.

The Scud attack marked an escalation in the two-month conflict and undermined Saudi Arabia’s announcement in April that it had destroyed the rebels’ missile arsenal. The coalition retaliated by bombing the headquarters of the pro-Houthi Yemeni army in the capital Sana’a, killing more than 40 people, according to the Saba news agency.

Saudi Arabia, the world’s top oil exporter, has said its military campaign in Yemen seeks to restore the rule of President Abdurabuh Mansur Hadi. The kingdom and its allies have portrayed the Houthis as tools of Shiite-ruled Iran, a claim viewed with skepticism by European and U.S. diplomats.

“The war was supposed to crush the Houthi movement and get them out of not only Aden but Sana’a and bring the former president back, and that’s clearly not happening,” Toby Matthiesen, a research fellow at the University of Cambridge and author of “The Other Saudis: Shiism, Dissent and Sectarianism,” said by phone.

Former President

The rebels are being aided by former President Ali Abdullah Saleh and have taken over large swaths of the country, a small oil producer but one located on an important oil transit route.

The latest escalation risks undermining efforts by the United Nations to hold peace talks in Geneva, due to start on June 14. The Houthis and Hadi’s government said they’ll attend the meeting.

“It definitely eliminates the possibilities of peace and a cease-fire, there’s no doubt about that,” Farea Al-Muslimi, a visiting scholar at the Carnegie Middle East Center in Beirut, said of the escalation. The Saudis “will go as far as they need to,” he said by phone from Riyadh, the Saudi capital.

The previous attempt by the UN to convene talks last month failed when Hadi’s government refused to attend unless the Houthis withdrew from cities and disarmed.

More than 70 people were wounded in the airstrike on the army’s headquarters, reported Saba, which is controlled by the Houthis. Warplanes also struck a rocket system southwest of the capital and an ammunition depot on Mount Nuqum, west of Sana’a. There were airstrikes in other provinces, including Saada, Amran, Aden, al-Dali, and Abyan.

Counting Scuds

Saudi officials “were shocked” by the Scud attack, Al-Muslimi said.

“I don’t think anybody knows how many missiles the Houthis have,” Gregory Gause, a professor of international affairs at Texas A&M University, said by e-mail. Al-Muslimi said Satellite imagery shows the Houthis repositioned some of the Yemeni army’s 300 Scud missiles and directed them at Saudi Arabia, a Gulf diplomatic official said in March.

Saudi Arabia and neighboring Gulf states, including the United Arab Emirates, spent billions of dollars over the past decade boosting their missile defenses with the latest upgrades of the Raytheon Co.-built Patriot and other anti-missile systems.

The Yemen bombing campaign began two months after King Salman ascended to the throne in Saudi Arabia in January following the death of his brother King Abdullah. Since then, he shuffled his cabinet twice and named his son, Prince Mohammed Bin Salman, as defense minister and deputy crown prince, making him second in line to the throne.

The new Saudi leadership “is really invested in this war,” Matthiesen said. “So something needs to come out of this for them and for Mohammed Bin Salman, in particular.”