Saudi Arabia's missile interceptions came hours after Saudi air defences shot down two unmanned Yemeni drones in southern Saudi Arabia..
The company is building a 400,000-barrel-per-day refinery in Jizan, part of a new economic city on the Red Sea, which is expected to become fully operational in 2019.
There was no immediate comment from the government but according to Saudi news channel al-Arabiya, the explosions were caused by the Saudi air defence intercepting a rocket.
Syria, Russia accuse Israel over strike on Syrian air base
The European Union also said evidence pointed to the use of chemical weapons by Assad's forces. It is believed the strikes are in response to an alleged chemical gas attack on Saturday.
The missile is thought to have been fired by Houthi rebels in Yemen, who a Saudi-led coalition has been bombing since March 2015, when it intervened in support of ousted President Abdrabbuh Mansour Hadi in an effort to prevent Houthis from maintaining the capital of Sanaa.
The coalition has launched thousands of air strikes in Yemen which have hit schools, markets and hospitals, killing hundreds of people - though it says it does not target civilians.
The Houthis have stepped up ballistic missile attacks on the kingdom in what it says is retaliation for the air raids.
The arms monitor Conflict Armament Research (CAR) said it had evidence showing the Qasef-1 and other Houthi kit was made in Iran and was not of indigenous design and construction "in contrast to Houthi statements".
Saudi coalition spokesman Turki al-Maliki accused rival Iran of being behind Wednesday's attacks.