Yemen's Iran-aligned Houthis have stepped up missile and drone attacks on Saudi Arabia this week in a resurgence of tactics that had largely subsided since late last year amid United Nations-led peace efforts.
The latest hostilities coincide with rising tensions between Iran and Gulf Arab states allied to the United States and come just as a sensitive, U.N.-sponsored peace deal is being carried out in Yemen's main port of Hodeidah, a lifeline for millions.
The Houthis, who claimed responsibility for last week's armed drone strikes on oil assets in Saudi Arabia, said on Tuesday that one of their drones hit an arms depot at the kingdom's Najran aiport near the Yemeni border, causing a fire.
The Saudi-led military coalition said a civilian facility in Najran province was targeted with an explosive-laden drone.
It said on Monday that Saudi defence forces intercepted Houthi ballistic missiles fired towards Mecca, Islam's holiest site. The Houthis denied doing so.
On Sunday, the Houthis said they would attack 300 vital military targets in Saudi Arabia, the United Arab Emirates and Yemen.
Saudi Arabia and the UAE head a coalition that intervened in Yemen in 2015 to try to restore the internationally recognised government ousted from power in the capital Sanaa by the Houthis in late 2014.
The movement has during the war repeatedly targeted Saudi cities and vital installations - mostly in border areas, but on several occasions the capital Riyadh as well. The Houthis pledged last November to stop attacks on Saudi Arabia and the UAE at the request of the United Nations.
While attacks on Saudi border areas continued, the Houthis had avoided targeting major cities or infrastructure. There have been no reports of attacks on the capital since last June.
The coalition has in return conducted multiple air strikes on the Houthi-held Yemeni capital Sanaa which it says target military facilities and aim to neutralise the group's ability to fire missiles and drones.
Riyadh and Abu Dhabi accuse Iran of arming the Houthis, a charge denied by the group and Tehran.