Iran and Hezbollah have trained Houthi militias to harm Yemenis, claimed a spokesperson for the Saudi-led coalition against the rebels, citing the ability of militias to operate fighter jets.
"We have evidence that Iran trained Houthi militias on operating fighter jets," Saudi Brigadier General Ahmed Asiri told reporters, noting that militia cannot on their own have picked up the skills.
Houthi fighters seized the capital Sanaa six months ago and launched an offensive in the south, backed by army units loyal to former ruler Ali Abdullah Saleh.
The Saudi-coalition alleges that the rebels are proxies for regional Shiite powerhouse Iran seeking to destabilise the region following success in Syria, Lebanon and Iraq.
Tehran has denied that it is supplying the rebels with some logistical aid and supplies.
Almost two weeks since the coalition began bombing Houthi targets, the battle continues to intensify. The civilian situation in Yemen has provoked UN and aid agencies to announce a humanitarian crisis.
Hospitals are under-equipped to deal with overflowing numbers of injured as basic supplies of water and power have been affected in many areas.
An initial International Committee of the Red Cross flight transporting medical personnel has reached the Yemeni capital Sanaa, reported AFP on 7 April. A cargo plane with 17 tons of medical supplies was in the Jordanian capital, Amman, awaiting the go-ahead from coalition forces to land in Sanaa, hopefully on 8 April.
Around 560 people, including dozens of children, have been killed, and more than 1,700 people wounded while 100,000 have fled their homes as fighting intensified, said the WHO.
Children have been especially vulnerable, said Unicef.
Violence has disrupted water supplies in areas of southern Yemen and sewage is overflowing in some locations, raising the risk of outbreaks of disease.
The Saudi-led coalition of Gulf nations is backing forces loyal to former president Abdrabbuh Mansour Hadi who fled the nation after the Shiite rebels took over.