Arab coalition warplanes bombed rebel camps in Yemen Friday in a second straight day of strikes led by Saudi Arabia, which accused Iran of "aggression" across the region.
A months-long rebellion by Shia fighters has escalated into a regional conflict that threatens to tear apart the impoverished state at the southern tip of the Arabian Peninsula.
Sunni-ruled Saudi Arabia has vowed to do "whatever it takes" to prevent the fall of its ally President Abedrabbo Mansour Hadi, accusing Shia Iran of backing the Houthi rebels' power grab.
At least 39 civilians have been killed in more than 24 hours of Saudi-led air strikes against the Houthis, officials at the rebel-controlled health ministry in the capital said.
Twelve of the victims died when surrounding residential areas were hit in a raid against a military base north of the capital, the officials told AFP.
At dawn on Friday, three air strikes hit the presidential compound in south Sanaa which the rebels seized last month, witnesses said.
They also bombed a Houthi-controlled army brigade in Amran province, north of the capital, and arms depots in the northern rebel stronghold of Saada, residents said.
The conflict has thrown up a major hurdle to Washington's longstanding drone war against Al-Qaeda militants who have exploited the power vacuum in Yemen since a 2011 uprising.
Hadi, backed by the West and Gulf Arab states, arrived in Riyadh on Thursday with officials saying he was on his way to Egypt to take part in a two-day Arab League summit at the weekend.
It was the first confirmation of his whereabouts since the rebels began advancing this week on the main southern city of Aden, where the president had been holed up since fleeing Sanaa last month.
Saudi Arabia says more than 10 countries, including four other Gulf monarchies, have joined the anti-Houthi coalition.