Saudi Arabia and Gulf region allies launched military operations including air strikes in Yemen on 26 March, officials said.
Unidentified warplanes launched air strikes on the main airport in the Yemeni capital, Sana'a, and its al Dulaimi military airbase, residents said.
A witness in the capital said four or five houses near Sana'a airport had been damaged. Rescue workers put the death toll from the air strikes at 13, including a doctor who had been pulled from the rubble of a damaged clinic.
One witness, Mohamed, said bodies were still buried under the rubble, with only six recovered from a building which was hit. Another witness confirmed there were more bodies under the rubble.
Gulf broadcaster al-Arabiya TV reported that Saudi Arabia was contributing as many as 150,000 troops and 100 warplanes to counter Iran-allied forces besieging the southern city of Aden where the US-backed Yemeni president had taken refuge. Egypt, Jordan, Sudan and Pakistan were ready to take part in a ground offensive in Yemen, it said.
There was no immediate confirmation of those figures from Riyadh. Al-Arabiya also said the United Arab Emirates was sending 30 warplanes to join the operation, along with 15 each from Bahrain and Kuwait, 10 from Qatar, six each from Jordan and Morocco and three from Sudan.
Yemen's slide towards civil war has made it a crucial front in mostly Sunni Saudi Arabia's rivalry with Shi'ite Iran, which Riyadh accuses of stirring up sectarian strife throughout the region and in Yemen with its support for the Houthis.