An attack by Yemeni Houthi rebels on an oil refinery in the port city of Aden has sparked a fire at a storage tank that may spread, threatening supplies, said Naser Shaif, a spokesman for the Aden Oil Refinery Co. The missile attack that hit the refinery, which is under the control of pro-government fighters, on Monday set off a “very serious” blaze that may reach another 100 storage tanks holding 1.2 million tons of oil and fuels, Shaif said by phone. A coalition led by Saudi Arabia has been conducting air strikes in Yemen targeting the Shiite rebels since March after the group ousted President Ali Abdullah Saleh. While the Saudi military intervention in the conflict hasn’t succeeded in reversing gains by the rebels, who control the capital, Sana’a, the government-in-exile has allied with fighters in Aden.