The developments mark a new escalation in Yemen's six-year conflict between the coalition-backed Yemeni government and the rebels, despite a renewed US push to end the conflict.

The strikes triggered huge explosions in Sanaa and sent plumes of smoke rising in the sky, according to AFP correspondents at the scene. The rebels reported seven air strikes on the city.

"The military operation targets Huthi military capabilities in Sanaa and a number of other provinces," the coalition was quoted as saying by the official Saudi Press Agency.

The raids come after the coalition said it intercepted a total of 12 drones launched by the rebels on Sunday, in a sharp escalation in cross-border attacks on the kingdom.

The coalition -- fighting in Yemen alongside the internationally recognised government against the insurgents -- said the drones were aimed at "civilian" targets in Saudi Arabia, SPA reported, without specifying the locations.

Targeting civilians in the kingdom was a "red line", the coalition said after the retaliatory strikes on Sanaa.

Amid a new US push for a resolution to the grinding conflict, it added that the Huthis' actions "will not lead to an imposition of a political settlement".

The rebels did not immediately claim responsibility for the drone attacks.

- 'Beyond humanitarian assistance' -

The grinding conflict has claimed tens of thousands of lives and displaced millions, according to international organisations, sparking what the United Nations calls the world's worst humanitarian crisis.

On Sunday, David Gressly, the UN's humanitarian coordinator for Yemen, was in the Red Sea port of Hodeida, a key entry point for both humanitarian aid and commercial goods.

"I need to understand the situation of food, fuel, health, water, education and other needs of the people," he told reporters. "What we would want to see is the port to be open, not only for fuel but other commodities."

The UN had warned of a "death sentence" against Yemen after a donor conference last week yielded less than half the funds needed to prevent a devastating famine.

It appealed for $3.85 billion to pay for urgently needed aid, but just $1.7 billion was offered at the virtual pledging conference.

"After over a year of Covid throughout the world, the economies are weak and those who are giving funding find it more difficult to give money," said Gressly.

"So we need to find a way to go beyond humanitarian assistance to help the economy come back."

- Escalation in fighting -

The Huthis have stepped up attacks on Saudi Arabia in recent weeks, while they escalate an offensive in Yemen to seize the government's last northern stronghold of Marib.

The escalation comes after the United States last month delisted the Huthis as terrorists and stepped up efforts to de-escalate the six-year conflict.

The terror designation, imposed late in the administration of former US president Donald Trump, had been widely criticised by aid organisations, who warned it would hamper their efforts to alleviate a humanitarian crisis in Yemen.

"The removal of the Huthis from the list of terrorist groups has been interpreted in a hostile way by the militia," SPA cited the coalition as saying.

The coalition added that their "victories" in Marib had prompted the rebels to step up attacks on the kingdom.

On Saturday, Yemeni government sources said fierce fighting between pro-government forces and the rebels in oil-rich Marib had left at least 90 combatants on the two sides dead over the span of 24 hours.

Years of bombing have failed to shake the rebels' hold on Sanaa, and they have steadily expanded their reach in the country's north.

US President Joe Biden has halted support to Saudi offensive operations in Yemen's war, which he called a "catastrophe" that "has to end".

But he has also reiterated US support for Saudi Arabia in defending its territory.