According to witnesses, strikes hit the rebel-held presidential compound in south Sanaa on Friday, as well as various military sites outside the capital including rocket launchers at the airport.

Sunni-ruled Saudi Arabia vowed on Friday to do "whatever it takes" to prevent Yemen's embattled President Abedrabbo Mansour Hadi from being overthrown. The kingdom also accused Shiite Iran of "aggression" and of backing a months-long rebellion by Shiite fighters.

Also involved in the attacks were eight other Arab states, including the United Arab Emirates and Egypt. It was not clear, however, which of the allies carried out the strikes.

Despite the Saudi-led attacks on Friday, Yemen's Houthi rebels continued to make wide gains in the countries south and east.

The spiraling violence has triggered fears that Yemen is becoming a battleground for a sectarian proxy war between Sunni Saudi Arabia and Shia Iran.

'Lasting stability'

The White House said on Friday that Obama had offered his support for the airstrikes during a phone call with Saudi ruler, King Salman.

"The president and King Salman agreed that our collective goal is to achieve lasting stability in Yemen through a negotiated political solution facilitated by the United Nations and involving all parties as envisioned in the GCC Initiative," National Security Council spokeswoman Bernadette Meehan said in a statement.

Saudi pilots rescued

Obama's pledge of support on Friday followed the rescue of two Saudi pilots on Thursday by US military. The pilots ejected themselves from their jet off Yemen's coast during the ongoing strikes. The reason why their plane went down in international waters is not yet clear.

According to officials at the rebel-controlled health ministry in Sanaa, at least 39 civilians have been killed in operation Decisive Storm, as the Saudi-led offensive is called.

ksb/bk (AFP, AP, Reuters)