One Egyptian was killed and two of his countrymen were wounded by falling shrapnel in Riyadh, authorities said, with residents reporting loud explosions and bright flashes in the sky shortly before midnight.

The Iran-aligned Huthi rebels fired three missiles at Riyadh and four others at the southern cities of Khamis Mushait, Jizan and Najran, with the coalition saying they all targeted populated areas.

"This aggressive and hostile action by the Iran-backed Huthi group proves that the Iranian regime continues to support the armed group with military capabilities," coalition spokesman Turki al-Malki said.

"The firing of multiple ballistic missiles towards cities is a serious development."

The Huthi-run Al-Masira television channel claimed the rebels had targeted Riyadh's King Khalid International Airport as well as other airstrips in the south of the kingdom.

The strikes come after the US defence secretary last week urged Saudi Crown Prince Mohammed bin Salman during his visit to Washington to pursue "urgent efforts" to end Yemen's wrenching conflict.

The Huthi rebels have fired dozens of missiles into Saudi Arabia since last year, all of which Saudi forces claim to have intercepted, underscoring their capacity to strike deep within the kingdom amid a stalemated war in Yemen.

The latest attack could further escalate the coalition's military campaign.

A major attack targeting Riyadh international airport on November 4 triggered the tightening of a longstanding Saudi-led blockade of Yemen -- already on the verge of famine.

Another strike on December 19 targeted Riyadh's Yamamah palace, the official residence of King Salman.

- Humanitarian crisis -

Saudi Arabia has accused its arch foe Iran of supplying the missile to the rebels, a charge Tehran strongly denied.

The Huthis expelled pro-government forces from the capital in September 2014 and went on to seize swathes of the impoverished Arabian peninsula country.

This prompted a military coalition led by Saudi Arabia to intervene in Yemen on March 26, 2015, to help the government push back the Shiite rebels.

Since then, around 10,000 people have been killed and 53,000 wounded in Yemen, triggering what the United Nations has called the world's worst humanitarian crisis.

Huthi rebel chief Abdelmalik al-Huthi on Sunday said his fighters were ready to make more "sacrifices" against the Saudi-led coalition, in an address marking the war's third anniversary.

The Huthis plan a huge rally in Sanaa on Monday to mark the anniversary.

The UN says living conditions in the war-scarred country have reached catastrophic levels and that 8.4 million people face imminent famine.

The UN urgently needs $350 million for humanitarian projects in Yemen, a senior agency official said on Sunday, insisting it was mere "peanuts" compared with the cost of the country's war.

Saudi Arabia and its allies -- aided by billions of dollars worth of military equipment from the US and Britain -- could stand guilty of war crimes, Amnesty International said on Friday.

Numerous rounds of UN-sponsored peace talks have failed to stem the bloodshed in Yemen.