Forces loyal to Yemen's exiled president, backed by Saudi-led air and naval support, recaptured the airport in second city Aden after a four-month battle with Iran-backed rebels, military sources said.

Fighting in the port city escalated as UN chief Ban Ki-moon expressed disappointment that a UN-declared ceasefire failed to take hold over the weekend.

The retreat by the Shiite rebels came as Iran -- regarded as their main foreign supporter -- struck a historic deal with world powers to curb its nuclear programme.

Hours after the deal was signed, Saudi Arabia's King Salman spoke with US President Obama about both the Iran deal and the urgent need to end the conflict in Yemen, which has killed more than 3,200 people since late March.

The two leaders "spoke about the urgency of stopping the fighting in Yemen and the importance of ensuring that assistance can reach Yemenis on all sides of the conflict", the White House said.

Leading Sunni kingdom Saudi Arabia has been deeply concerned about Shiite Iran's influence in Riyadh's impoverished southern neighbour and leads an Arab coalition which has since March bombed the rebels and their allies in the armed forces.

The coalition earlier denied its warships pounded the rebels as they pulled back from positions they had held in Aden since forcing President Abedrabbo Mansour Hadi into exile.

Saudi Brigadier General Ahmed al-Assiri, spokesman for the coalition, also downplayed the loyalists' airport seizure.

"We don't want to claim victory because it is a step, not more than that," he told AFP.

"They have a lot of work to do to secure positions that they control today."

Hadi was personally supervising "Operation Golden Arrow for the Liberation of Aden", said his chief of staff, Mohammed Marem.

Aden airport had been held by rebels since soldiers of the 39th Armoured Brigade defected on March 25.

The Huthis and their allies later seized the presidential palace and Aden's main commercial port.

Military sources in Aden said pro-Hadi fighters were benefiting from ground support by Yemeni forces trained in Saudi Arabia, in addition to sophisticated weapons delivered by the coalition.

"Forces recently trained in Saudi Arabia are strongly participating in the fighting alongside the Popular Resistance," said one source, referring to the southern militia that has been the mainstay of Hadi's support.

Retaking Aden airport is the first significant achievement for loyalist fighters since the president fled.

Assiri said "it's normal" for the coalition to be providing training, equipment and information to the local fighters on the ground.

- Ban 'very disappointed' -

The rebels overran the capital Sanaa unopposed in September and went on to seize much of the rest of the country, aided by troops still loyal to Hadi's ousted predecessor, Ali Abdullah Saleh.

Coalition air strikes targeted Sanaa, the rebels' northern stronghold of Saada and the Hijja region in the north, residents said.

Aden's oil refinery -- Yemen's biggest -- was ablaze on Tuesday after being hit by rockets during the fighting for the city. There were conflicting claims about which side caused the fire.

Fighting raged despite a UN-declared six-day ceasefire that was supposed to have taken effect shortly before midnight Friday.

The UN chief said he was "very much disappointed" by the failure of the truce but retained hope the fighting might still end, his spokesman said.

"We have not lost hope and discussions are ongoing," Stephane Dujarric said.

He defended the decision to call the ceasefire, saying UN envoy Ismail Ould Cheikh Ahmed "had received the commitments he felt were necessary for us to come out with this announcement".

But coalition spokesman Assiri said Hadi's government did not ask for a pause, Huthis had not committed to it and there was no "mechanism to monitor" and prevent violations.

The UN has declared Yemen a level-3 humanitarian emergency, the highest on its scale.

More than 21.1 million people -- over 80 percent of Yemen's population -- need aid, with 13 million facing food shortages, while access to water has become difficult for 9.4 million people.

Despite the fighting, refugees from the Horn of Africa continue to arrive in Yemen, the UN High Commissioner for Refugees said in Geneva.

Johannes Van Der Klaauw, the UN's humanitarian coordinator for Yemen, said 37,000 migrants arrived this year -- almost one-third of them after the coalition began its air strikes.
Source: AFP