ADEN (AFP) - Yemeni rebels closed in on President Abedrabo Mansour Hadi as they seized Aden's airport on Wednesday, prompting warnings of a full-blown conflict and pleas for urgent foreign intervention.

The escalating turmoil in Yemen - which borders Saudi Arabia and lies close to key shipping routes - pushed up world oil prices on fears it could threaten Middle Eastern petroleum producers.

Acting foreign minister Riyad Yassin warned in Egypt that the fall of second city Aden would mean the "start of civil war" as he drummed up Arab military support for Hadi.

His comments came as army units switched allegeance to the rebels and seized Aden's international airport.

Aides to Hadi said, however, that the Western-backed president had been taken to a safe haven "within Aden", where he fled last month.

One of his advisers said former president Ali Abdullah Saleh was the man pulling the strings as the rebels advanced.

"The Huthis are puppets in the hands of Saleh," the Riyadh-based Yassin Makkawi told AFP.

Washington said it had been in touch with Hadi and that he was no longer at his residence, but it was unable to say where he was.

Yemen has been gripped by growing turmoil since the Shiite Huthi rebels launched a power takeover in Sanaa in February.

The strife has raised fears Yemen could be torn apart by a proxy war between Shiite Iran, accused of backing the rebels, and Sunni-ruled Saudi Arabia, which supports Hadi.

'DAGGER' IN SAUDI SIDE

Acting foreign minister Yassin warned that domination by Iran would be a "dagger in the side of Saudi Arabia and the rest of countries of the Gulf".

His comments came after the Huthis said they had captured his defence minister in their push southwards.

Missiles were fired from an unidentified warplane at Hadi's complex in Aden, but only hit an abandoned building, a presidential security official said.

Large crowds of Aden residents could be seen running to take up arms at a weapons depot in preparation for the expected rebel advance.

As the security situation worsened, Aden's international airport suspended operations.

In the afternoon, the 39th Armoured Brigade posted near Aden airport took control of the facility in support of the rebels, witnesses said.

Rebel television said the unit had "secured the airport".

Hadi appealed to the UN Security Council on Tuesday to "shoulder its responsibilities... to safeguard Yemen from sliding into more chaos and destruction."

His plea followed a warning from UN envoy Jamal Benomar that Yemen was sliding towards a "civil war".

Rebels seized a key airbase 50km north of Aden on Wednesday, days after US military personnel were evacuated.

Yemen has allowed Washington to wage a long-standing drone war against Al-Qaeda in the country.

The Huthis took control of Al-Anad airbase following "limited clashes" with pro-Hadi forces, an official said.

Rebels advanced deep into Lahj province, adjacent to Aden and where they said they had seized Hadi's defence minister, General Mahmud al-Subaihi.

HADI ALLY SEIZED

Subaihi, who escaped house arrest in Sanaa this month, had been seen as a vital ally of Hadi in charge of organising Aden's defence lines.

Dozens of people have been killed as the Huthis backed by troops allied to former strongman Saleh, have clashed with pro-Hadi forces as they push southwards.

Saleh, who resigned in 2012 following nationwide protests, has been accused of backing the Shi'ite rebels as he seeks to regain influence.

Yemen is increasingly divided between a north controlled by the Huthis and a south dominated by Hadi supporters.

In a letter to the Security Council Tuesday, Hadi called for a binding UN resolution asking countries to provide immediate support "by all means and measures" to protect Yemen.

He voiced concerns that Al-Qaeda will "seize the current instability to spark further chaos".

He referred to an unspecified "missile capability looted from the legitimate authority," and asked the Security Council to take control of the missiles.

The Council has so far only released a declaration of support for Hadi, during an emergency meeting the president requested Sunday.

Diplomats said no new meeting has been planned at this time.

Yassin told reporters in Egypt that he would call for "urgent intervention" at an Arab League summit due to start on Saturday.

Saudi Foreign Minister Prince Saud al-Faisal has warned that Arab countries might take action "to protect interests from Huthi aggression".