The Houthis, an Iranian-backed militia, said they had fired a wave of missiles and drones at Riyadh, where residents reported explosions, and on Saudi oil facilities. Saudi Arabia has not commented on the claims. Smoke rising on Saturday above Riyadh, the Saudi capital.

The Houthi militia in Yemen said on Saturday that it had attacked Saudi Arabia’s capital and oil facilities with a barrage of missiles and drones, a significant escalation in the renewed war between the kingdom and the Iranian-backed group. Saudi Arabia has not publicly commented on the Houthis’ claim. But the capital was on edge.

Emergency alerts sounded in Riyadh earlier on Saturday, with residents reporting loud explosions, and flights were severely disrupted at the city’s airport. There were no immediate reports of casualties. Yahya Saree, a spokesman for the Houthi military, said the group had fired a “large number of ballistic and cruise missiles and drones” targeting “sensitive sites” in Riyadh and facilities for Saudi Arabia’s national oil company in Yanbu, a crucial Red Sea terminal. Mr. Saree said the attacks were retaliation for more than 700 Saudi airstrikes in Yemen, where the kingdom has been backing government forces trying to wrest back territory from a lightning Houthi offensive.

Saudi Arabia has not acknowledged launching any airstrikes in recent days, and Saudi officials generally say that such strikes are being carried out by the Saudi-backed Yemeni government. The Saudi authorities did not respond to a request for comment on Saturday. Starting in 2015, Saudi Arabia led a disastrous bombing campaign to rout the Houthis but failed to push the group out of power, leaving Yemen in fragmented control of government forces and the militants.

A truce reached in 2022 has unraveled amid worsening fighting in recent months, as the Houthis have sought to seize strategic territory in Yemen and enforce a naval blockade on Saudi Arabia in the Red Sea. But the attacks on Riyadh were a “huge” escalation, said Farea Al-Muslimi, a Yemen specialist at Chatham House, a London-based research group. He said they reflected that the “Houthis are not going to stop anywhere,” particularly at a time when they feel emboldened by recent battlefield victories.

In his statement, Mr. Saree, the Houthi military spokesman, said that the group was pursuing a policy of “escalation for escalation” until Saudi Arabia stops its “aggression” in Yemen and lifts restrictions on Yemeni airspace, which the militia refers to as a blockade. Flight Radar24, a flight tracking website, showed major delays on Saturday afternoon at the King Khalid International Airport in Riyadh. Photographs and video by the Reuters news agency showed a plume of smoke rising in the vicinity of the airport.

Overnight, Riyadh residents received two emergency alerts warning of a “hostile aerial threat.” On Saturday, two booms rattled western Riyadh, home to a diplomatic quarter hosting foreign embassies. Saudi Civil Defense officials said early-warning systems were also activated in nine other cities. It was the first time alerts were sounded in Riyadh since tensions with the Houthis flared in July.

Recent strikes had largely targeted southern Saudi cities, sparing the capital, where Crown Prince Mohammed bin Salman of Saudi Arabia is scheduled to host the Future Investment Initiative, a major gathering of billionaires and international financiers, next month. The reported explosions in Riyadh followed Houthi accusations on Friday that Saudi Arabia had attempted a “criminal” attack on Sanaa, the Yemeni capital, which the Houthis seized in 2014. Mr. Saree said the group had foiled...