Saudi air defences intercepted ballistic missiles over Riyadh and a city on the Yemen border late Saturday, leaving at least two civilians wounded in the capital that is under curfew in a bid to curb the spread of the coronavirus.

Multiple explosions shook Riyadh in the attack, which the Saudi-led military coalition blamed on Yemen's Iran-aligned Huthi rebels who have previously targeted Saudi cities with missiles, rockets and drones.

It was the first major assault on Saudi Arabia since the Huthis offered last September to halt attacks on the kingdom after devastating twin strikes on Saudi oil installations. "Two ballistic missiles were launched towards the cities of Riyadh and Jizan," the official Saudi Press Agency reported, citing the coalition fighting the rebels.

Their interception sent shrapnel raining on residential neighbourhoods in the cities, leaving two civilians injured in Riyadh, a civil defence spokesman said in a separate statement released by SPA.

There was no immediate comment from the rebels. At least three blasts rocked the capital, which is under a 15-hour coronavirus curfew, just before midnight, said AFP reporters. Jizan, like many other Saudi cities, faces a shorter dusk-to-dawn curfew.

The assault comes despite a show of support on Thursday by all of Yemen's warring parties for a United Nations call for a ceasefire to protect civilians from the coronavirus pandemic. Saudi Arabia, the Yemeni government and the rebels all welcomed an appeal from UN Secretary General Antonio Guterres for an "immediate global ceasefire" to help avert disaster for vulnerable people in conflict zones.

The call coincided with the fifth anniversary of Saudi Arabia's military intervention in Yemen's civil war, which was launched to shore up the internationally recognised government against the Huthi rebels.

Escalating conflict

The Yemen government condemned the attack, which it said undermined efforts to scale down the conflict amid the coronavirus outbreak. Information Minister Moammer al-Eryani said in a tweet that the strikes also confirmed the "continued flow of Iranian weapons" to the Huthi militias. "This militia lives only on wars and doesn't understand peace language," he said.

Yemen's broken healthcare system has so far recorded no case of the COVID-19 illness, but aid groups have warned that when it does hit, the impact will be catastrophic. The country is already gripped by what the UN calls the world's worst humanitarian crisis.

Saudi Arabia is also scrambling to limit the spread of the disease at home. The kingdom's health ministry has reported 1,203 coronavirus infections and four deaths from the illness so far. Fighting has recently escalated again between the Huthis and Riyadh-backed Yemeni troops around the strategic northern districts of Al-Jouf and Marib, ending a months-long lull.

The warring sides had earlier shown an interest in de-escalation, with a Saudi official saying in November that Riyadh had an "open channel" with the rebels with the goal of ending the war. The Huthis also offered to halt all missile and drone attacks on Saudi Arabia after strikes on its oil installations last September, which were claimed by the rebels but widely blamed on Iran, despite its denials.

But those efforts seem to have unravelled. Observers say the rebels may have used the lull to bolster their military capabilities. Riyadh had expected a quick victory when it led a multi-billion dollar intervention in 2015 to oust Huthi rebels, under a newly assertive foreign policy led by Crown Prince Mohammed bin Salman.

But the costly intervention has failed to uproot the rebels from their northern strongholds, while pushing the Arab world's poorest nation into a humanitarian crisis.