The Iran-backed Huthis have escalated attacks on the kingdom and Saudi-backed Yemeni forces days after the United States moved to delist the rebels as terrorists and stepped up efforts to de-escalate the six-year conflict.

A rebel drone early Thursday targeted the southern garrison town of Khamis Mushait that hosts a key airbase, but was destroyed before reaching its target, the official SPA news agency cited the coalition as saying.

Hours later, the coalition said it intercepted a rebel ballistic missile launched towards Khamis Mushait and another explosives-laden drone that targeted the kingdom's southern region.

The coalition did not report any casualties or damage.

The strikes come after the rebels mounted a drone attack on Abha international airport in the kingdom's southwest on Wednesday, leaving a civilian plane ablaze.

In a joint statement Thursday, Germany, Britain and France said they "strongly condemn" the airport attack, which they said was a "violation of international law".

The United States also denounced the assault, calling on the Huthis to "immediately stop these aggressive acts" and "constructively engage" in President Joe Biden's peace effort.

Biden, who has reversed his predecessor Donald Trump's policy on the conflict, has deployed his new Yemen envoy Tim Lenderking to Saudi Arabia.

On Wednesday Lenderking and his UN counterpart Martin Griffiths met Saudi Arabia's deputy defence minister, Prince Khaled bin Salman, who oversees the Yemen portfolio.

Separately, US Secretary of State Antony Blinken discussed the attack on Abha during a call with Saudi Foreign Minister Prince Faisal bin Farhan, SPA reported.

- 'Catastrophe' -

Biden has halted support to Saudi offensive operations in Yemen's war, which he called a "catastrophe" which "has to end". But he has reiterated US support for Riyadh in defending its territory.

Alongside the cross-border attacks, the Huthis have resumed an offensive to seize the Yemeni government's last northern stronghold of Marib.

The battle has centred on a government military base west of the city of Marib, a pro-government commander at the scene told AFP.

"The camp was taken by the Huthis but they were dislodged" by coalition air raids, he said, adding that losing the site would sever an important supply line for government forces.

Clashes at the base on Wednesday killed 23 insurgents and 15 pro-government forces, according to the commander.

Loudspeakers on mosques in Marib were used to urge local residents to join the fight or to donate cash, witnesses said.

After leading its allies into the conflict in 2015, Saudi Arabia is now stuck in a military quagmire.

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

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

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