A man looks at damage in his house caused by an April 20 air strike that hit a nearby army weapons depot in Sanaa April 21, 2015. [Photo/Agencies]

The Saudis called for a quick resumption of UN-facilitated talks to try to get a peaceful political arrangement for Yemen, which has a long history of internal fighting.

Saudi Arabia had earlier signaled a change in its mission by ordering its National Guard, widely regarded as the kingdom's best equipped military ground force, to join the campaign, but did not say what role it would play.

The bloodshed in Yemen, racked by fighting between factions supported by different regional powers, had continued earlier in the day. At least 40 people, most of them civilians, were killed in two air strikes.

One raid hit a security building in Haradh near Yemen's border with Saudi Arabia, killing seven soldiers and 13 civilians. Twenty people died in another strike in Ibb province when a bridge was hit as militia members drove across.

The Houthis and military units loyal to the powerful former president Ali Abdullah Saleh have taken swathes of territory and forced the current president, Abd-Rabbu Mansour Hadi, into exile in Saudi Arabia.

The conflict created desperate shortages of food and other supplies in Yemen, where sea and airports are closed. Houthi politburo member Mohammed al-Bukhaiti accused the United States of worsening the "siege" on the country by sending warships to the waters off Yemen.