SANAA, July 28 (Xinhua) -- The Saudi-led coalition fighting Houthi rebels in Yemen launched a series of airstrikes on rebel-held sites in the capital Sanaa on Sunday evening, residents said.

The airstrikes targeted a military camp in Kutbayn area in Nehm district northeast of the capital and another camp in Aroush area of Khawlan district in the southeast of Sanaa.

Explosions could be heard in downtown Sanaa but there were no reports of casualties yet.

The coalition airstrikes came hours after the Yemeni Houthi rebels claimed launching a ballistic missile and bomb-laden drones attacks on the headquarters of the Saudi-led coalition and airport in the Saudi southwestern border city of Najran. The coalition, however, has yet to confirm the rebels' alleged attacks on Najran.

Houthis have recently stepped up missile and drone attacks on Saudi Arabia, but most of the missiles and drones were intercepted and destroyed by the kingdom's air forces.

Saudi Arabia has been leading an Arab military coalition against Iran-allied Houthis in Yemen for more than four years in support of the exiled internationally-recognized government of Yemeni President Abd-Rabbu Mansour Hadi.