(Reuters) - Yemen's Houthi rebels made broad gains in the country's south and east on Friday despite a second day of Saudi-led air strikes meant to check the Iranian-backed militia's efforts to overthrow President Abd-Rabbu Mansour Hadi.

Shi'ite Muslim Houthi fighters and allied army units gained their first foothold on Yemen's Arabian Sea coast by seizing the port of Shaqra 100km (60 miles) east of Aden, residents told Reuters.

Explosions and crackles of small gunfire rang out across Aden late on Friday as Houthis made a push on the southern port city's airport, a witness said.

The advances threaten Hadi's last refuge in Yemen and potentially undermine the air campaign to support him.

"The operation will continue as long as there is a need for it to continue," Asseri said.

Warplanes targeted Houthi forces controlling Yemen's capital Sanaa and their northern heartland on Friday. Asseri said that planes from the United Arab Emirates had carried out their first strikes in the past 24 hours.

In a boost for Saudi Arabia, Morocco said it would join the rapidly assembled Sunni Muslim coalition against the Houthis. Pakistan, named by Saudi Arabia as a partner, said it had made no decision on whether to contribute.