Yemen's Houthi militiamen, supported by army units, gained ground in the southern city of Aden on Sunday, pushing back loyalists of the Saudi-backed President Abd-Rabbu Mansour Hadi.

Residents took refuge in their homes and reported hearing sporadic gunfire and blasts of rocket-propelled grenades, and one witness saw a Houthi tank in the downtown Mualla district, which sits astride Aden's main commercial port.

Houthi forces have inched forward in street-fighting in the city despite an 11-day nationwide bombing campaign by a Saudi-led coalition aimed at halting the Iran-allied group and protecting Hadi's last bastion of support in the country.

Saudi planes parachuted weapons to Hadi's armed supporters there on Friday, helping them temporarily beat back Houthi advances.

The crates of light weapons, telecommunications equipment and rocket-propelled grenades were parachuted into Aden's Tawahi district, on the far end of the Aden peninsula which is still held by Hadi loyalists, fighters told Reuters.

Saudi Arabia has said defending Aden's government is a "main objective" of its mission and Hadi's administration has called for a foreign ground intervention into the beleaguered city.

Adel al-Jubeir, Saudi ambassador to the United States, said sending ground troops remained "on the table" and the operation's spokesman Brigadier General Ahmed Asseri declined to comment on media reports of Saudi special forces there.

In six months of fighting, the Shi'ite Muslim Houthis have seized much of Yemen's north and center but have faced stiff resistance in the country's Sunni south, raising fears of a sectarian civil war.

In the city of Lawdar about 200km east of Aden, 10 Houthi fighters and allied soldiers were killed in clashes which also killed four local tribesmen on Sunday, residents said.