Yemen's Iran-backed Houthi rebels captured more strategic islands in the southern Red Sea, government and Houthi officials said Monday, strengthening their control of a major maritime shipping route.

The capture of the islands of Greater and Lesser Hanish is the latest in the rebels' swift advance around the Bab el-Mandeb Strait, a key passage for Saudi oil shipments that has only become more crucial during the Iran war since it serves as an alternative to the Strait of Hormuz.

Yemen's Houthis said Monday they had fired dozens of drones and ballistic missiles at military targets in Saudi Arabia, in retaliation for airstrikes by Riyadh.

"The Yemeni armed forces conducted a large-scale military operation targeting military installations and infrastructure, including fighter jet hangars, radars, runways, ammunition depots, and other targets located at King Khalid Air Base in Khamis Mushait," said Houthi military spokesman Yahya Saree.

Iran's foreign ministry on Monday denied the country had any involvement in the war in Yemen, after the Iran-backed Houthi movement seized more territory.

"Iran does not interfere in Yemeni affairs," ministry spokesman Esmaeil Baqaei told reporters, saying the Houthis are "entirely independent actors who make their decisions based on their own interests".

Iran said a planned meeting with Gulf countries in Oman on Monday to discuss the Strait of Hormuz was postponed at the request of Saudi Arabia, which cited the war in Yemen.

"It is true that Saudi Arabia asked for this meeting to be postponed," said foreign ministry spokesman Esmaeil Baqaei. "Invoking the Yemeni issue as the reason is a false pretext," he added at a press conference in Tehran attended by AFP.

President Donald Trump said Sunday that he will look into requests from families of Sept. 11 victims to release records that could shed light on Saudi Arabia's alleged role in the attacks 25 years ago.

Several families have long alleged that a group of extremist religious leaders in Saudi Arabia gained influence in the Saudi government and aided the hijackers. Fifteen of the 19 hijackers were Saudis, but the Saudi government has long denied any involvement in the attacks.

The conflict in Yemen intensified on Sunday, as government forces launched attacks against Iran-backed Houthi rebels along the Red Sea and Houthis fired into neighboring Saudi Arabia, which supports Yemen's government.

The Yemeni government vowed to send more forces to the Red Sea coast and one official conceded a "painful" defeat last week when Houthis captured the port city of Mokha and an island on the Bab el-Mandeb Strait, a crucial shipping alternative to the Strait of Hormuz.

Houthi fighters on Sunday said they used drones and missiles to attack a military base in southern Saudi Arabia as renewed fighting with Yemen's government forces forced growing numbers of civilians to flee.

Iraqi authorities announced on Sunday a timeline to reopen three crossings with Iran, a day after closing them following a drone attack originating from their shared border on a Saudi pipeline.

After the Friday night attack on the East-West pipeline, Baghdad sacked the military commander in Missan province near the Iran border, after authorities determined the drones were launched from there.

A ship was struck in the Strait of Hormuz on Sunday, killing one person and injuring three, local Iranian authorities said, as Tehran and Washington clash over the strategic waterway.

Iran's foreign ministry said the country would meet with Gulf states in Oman on Monday to discuss the strategic Strait of Hormuz, which the Islamic republic has blockaded during the Middle East war.