Washington warned Thursday it would not "stand by" while Iran supports rebels in Yemen, where a Saudi-led coalition pounded anti-government forces at the start of a third week of bombings.
In the most direct US criticism yet of Tehran's backing of the Shiite Huthi rebels, Secretary of State John Kerry said Washington would not accept foreign interference in Yemen.
President Abedrabbo Mansour Hadi fled Aden for Saudi Arabia during the Huthi advance and the city has since seen heavy clashes between pro- and anti-government forces.
Riyadh has accused Tehran, the major Shiite power, of backing the rebels in a bid to establish a pro-Iran state on its doorstep.
But Iranian Foreign Minister Mohammed Javad Zarif insisted his government wanted a swift end to the fighting, which has cost more than 640 lives since March 19, according to the World Health Organization.
- US starts refuelling flights -
Kerry, fresh from world powers striking a framework agreement with Iran on its nuclear programme, said Washington was not looking for confrontation with Tehran.
"But we're not going to step away from our alliances and our friendships and the need to stand with those who feel threatened as a consequence of the choices that Iran might be making."
In another sign of growing US support for the Saudi effort, the Pentagon said it had started daily aerial refuelling for warplanes in the coalition.
The air strikes killed at least 14 rebel fighters in
Air strikes also hit a military camp in the southern Shabwa province that was seized by the Huthis' main allies -- security forces who have remained loyal to former strongman Ali Abdullah Saleh, a local official said.
- Diplomatic efforts -
As well as the Huthis, who hail from Yemen's north, the government has struggled against Al-Qaeda in the Arabian Peninsula (AQAP), considered the most dangerous of the jihadist network's branches.
Authorities in Yemen had for years allowed Washington to carry out a drone war against AQAP but US forces pulled out of the country amid the latest unrest.
Al-Qaeda has taken advantage of the chaos to seize control of some areas and carried out a series of deadly attacks on both government forces and the Huthis.
As the fighting and air campaign drag on, concern has been growing for what aid workers say is a mounting humanitarian crisis.
Some aid trickled in to Aden by ship on Wednesday but efforts by the International Committee of the Red Cross to organise flights of cargo planes into Sanaa have so far failed.
In Aden, witnesses have said the situation is dire, with bodies lying in the streets and mosques calling through loudspeakers for help.
Diplomatic efforts have stepped up to resolve the conflict, with the Iranian and Pakistani foreign ministers pledging at talks in Islamabad on Wednesday to work to find a negotiated solution.
Source: AFP Photo: AFP