Yemen's Shiite Huthi rebels said their cross-border barrage marked the launch of what their leadership has dubbed "the year of ballistics".

The attacks prompted swift condemnation from a Saudi military spokesman, who said the kingdom would respond "with resolve".

A missile launched from Sadaa, the Huthis' stronghold in northern Yemen, "towards Riyadh was successfully intercepted" by Saudi air defences, said Colonel Turki al-Malki, spokesman for a Saudi-led coalition fighting the Huthis.

The announcement came after an AFP journalist witnessed explosions and heard three blasts over the capital, which has come under repeated attack by Huthi rebels.

Malki said Saudi forces also intercepted two missiles in the southern Jizan and Najran provinces, close to the border with Yemen.

Saudi Arabia has since March 2015 led a coalition of Arab states fighting to roll back the Huthi rebels in Yemen and restore its neighbour's internationally-recognised government to power.

Nearly 10,000 people have since been killed in the conflict, in what the United Nations has called the world's worst humanitarian crisis.

Saudi Arabia accuses its rival Iran of smuggling missiles to the Huthis -- a charge Tehran denies.

Wednesday's attacks were claimed by the rebels via their news outlet Al-Masirah.

"The missile force carried out a large-scale ballistic missile attack on various parts of Saudi Arabia," Al-Masirah said.

It named the defence ministry in Riyadh, King Abdullah Economic City in Najran and the Saudi Aramco facility in Jizan as the targets.

The Huthis said the attacks were timed to "inaugurate the ballistic year announced by the president".

Saleh al-Sammad, head of the rebels' supreme political council, in a speech earlier this week declared 2018 would be "the year of ballistics".

- Rebel drones -

As the announcement on the missile interceptions emerged, Malki also said in a separate statement that Saudi air defences had shot down two unmanned Yemeni drones in southern Saudi Arabia.

One of the drones was targeting the Abha international airport in Asir province, which led to a temporary suspension of air traffic.

Upon coalition inspection, "it turned out to be a hostile Huthi drone with Iranian components", Malki said.

A second drone was identified while approaching a "civilian object" in Jizan province, he added.

The Huthis claimed attacks on Abha airport and Saudi Aramco, located in Jizan, publishing an infographic of the "Qasef 1" drone on Al-Masirah.

Oil giant Aramco downplayed the attacks, saying its "operations and facilities, including our facilities in Jizan, are operating normally and safely".

But the Huthi leadership was electrified.

"We are stronger today than every before," Huthi military spokesman Sharaf Luqman said of the incursions into Saudi Arabia.

He called the drone attack on Abha airport a "strategic step" to "complement" the ballistic missile strikes.

"Every time we are bombed, we will target a corresponding Saudi facility," Luqman said.