The Saudi-led coalition has launched heavy airstrikes on Shiite rebels in Yemen, targeting camps and weapons depots in the rebel-held capital, Sanaa.

Yemenis awoke to the sound of explosions early Friday when warplanes targeted weapons caches in Noqum mountain, sending up bursts of flames and columns of smoke.

Airstrikes also targeted the rebels, known as Houthis, in Saada, their northern heartland. Witnesses saw Apache helicopters flying overhead that appeared to be targeting rebel vehicles. The witnesses spoke on condition of anonymity out of security fears.

The Houthis have carried out cross-border attacks from Saada, which borders Saudi Arabia.

Yemen's war pits forces loyal to the country's exiled president against the Iranian-supported Houthis and allied military units. A Saudi-led coalition began striking the Houthis from the air on March 26.