ADEN (Reuters) - Local fighters battling the rebel Houthi militia in Yemen's port of Aden stormed areas around the airport on Sunday in an operation supervised by the Saudi-led coalition, which also provided air support, the group's spokesman said.

"Special forces from the southern fighters have been prepared and trained for an operation to attack Aden airport," said Ali al-Ahmadi, spokesman for the Southern Popular Resistance.

Ahmadi retracted an earlier statement that 40-50 coalition special forces fighters had deployed alongside his militia and Saudi Arabia denied that a major ground operation was under way or that it had put non-Yemeni forces on the ground in Aden.

The coalition, which seeks to restore the government of President Abd-Rabbu Mansour Hadi, includes eight other Arab states and is receiving logistical support from the United States, Britain and France.

It has refused to rule out the eventual use of ground troops, but to date it has mostly used air power and some artillery on the Saudi border to bombard Iranian-allied Houthi militia and allied army units.

ANTI-HOUTHI HOTBED

Aden, a hotbed of anti-Houthi sentiment, has been a flashpoint since the war began on March 26, when the coalition began attacking Houthi forces opposed to Saudi-backed Hadi, who was based in Aden for several weeks before fleeing to Riyadh.

The world's top oil exporter and arch Sunni Muslim regional rival of Shi'ite Iran, Saudi Arabia says it is concerned for its own security and Yemen's stability after Shi'ite Houthi forces captured the capital and began advancing across the country, on its southern border, in September.

Fighting around Yemen has killed more than 1,000 people, including an estimated 551 civilians since the bombings started, the United Nations said on April 24. Its children's agency UNICEF said at least 115 children were among the dead.

The international monitoring group Human Rights Watch (HRW) said the Saudi-led coalition attacking Yemen had probably used cluster bombs which are banned by most countries.

"Credible evidence indicates that the Saudi-led coalition used banned cluster munitions supplied by the United States in air strikes against Houthi forces," HRW said in a statement.

Saudi Arabia's coalition spokesman was not immediately available to comment on the report.

In overnight fighting, warplanes from the coalition struck Sanaa's al Dulaimi military airbase, residents of the Houthi-controlled capital said. The aircraft also targeted a camp of forces loyal to former president Ali Abdullah Saleh, an ally of the Houthis, in Arhab district north of the city, the residents added. There was no immediate word on casualties.

In Aden, fighting continued in central Mualla and Khor Maksar districts, near the main commercial port, as well as in the city's north, around a military camp and the airport, where there have been clashes for three days, local sources said.

Iran, which backs the Houthis, does not recognise Hadi and has portrayed the air strikes as an intervention in Yemen's internal affairs.

REGIONAL TENSION

Commenting on reports that the coalition had deployed troops to Aden, Brigadier General Ahmed Asseri said the alliance had not started any major ground offensive in the city.

He told Reuters there were no non-Yemeni forces fighting in Aden, but said the coalition would continue to assist local militias and loyal tribes fighting the Houthis.

"All of these options are on the table and we use it to give those loyal (elements) the capabilities to be able to protect themselves and civilians," he said.

"If some such thing happens (a special forces operation), we cannot talk about it in the media."

(Additional reporting by Mohammed Ghobari in Cairo, Angus McDowall in Riyadh and Amena Bakr in Doha, Writing by William Maclean; editing by)