At least 20 Houthi rebels were killed on Sunday when Saudi-led coalition warplanes hit a missile depot in the Yemeni northwestern province of Hajjah, a Houthi security official told Xinhua."Nearly 20 fighters were killed and some others wounded in the targeted site," the official said, speaking on condition of anonymity.The depot exploded and caught fire after being hit by more than 10 airstrikes, the official said, without giving further details.The depot is located in a small military camp run by Houthi rebels in the al-Raboo area in Abs district, which provides military supplies to the fighters in Medi town, which borders Saudi Arabia. Sunday's attack is the latest of a series of airstrikes carried out by the Saudi-led coalition fighting the Houthi rebels in a war of more than two and a half years.The new escalation of tension came six days after the Houthis killed former President Ali Abdullah Saleh who had shifted side to ally with the coalition.The security situation in Sanaa has calmed down after the Houthis completely controlled the capital and defeated Saleh's armed supporters.The capital's residents began gradually returning to the markets and streets, as state employees resumed work in the ministries.On Saturday, the coalition airstrikes hit Yemen's main satellite TV station in the rebel-held capital and killed four journalists.The airstrikes also targeted two popular markets in the north of Sanaa and south of the Red Sea port city of Hodeidah, killing at least six people, according to local officials.The Saudi-led coalition intervened in Yemen's conflict in 2015 to back President Abd-Rabbu Mansour Hadi. The war in Yemen has killed over 10,000 people, mostly civilians, and displaced 3 million others, according to UN agencies.