Saudi-led coalition warplanes carried out fresh raids on rebel positions in southern Yemen Thursday as pro-government tribesmen advanced on Shiite Huthi strongholds in the north, tribal and army sources said.

On the political front, Iran said it backed UN-brokered efforts to relaunch political talks but was opposed to foreign interference in Yemen's conflict, in which it backs the rebels.

Coalition warplanes twice bombed a Huthi gathering on a hill overlooking Taez, from which rebels have been attacking residential neighbourhoods of Yemen's third city, a local government official told AFP.

He said four civilians were killed and six wounded in overnight mortar fire by the rebel forces -- Huthis and renegade troops loyal to former president Ali Abdullah Saleh.

The warplanes also struck rebel positions in nearby Daleh as well launching three dawn raids on Al-Anad air base in the southern province of Lahj, military sources said.

Arms depots of pro-Saleh forces at Dhamar and Baida provinces in central Yemen also came under air attack several times, residents said.

In main southern city Aden, witnesses reported sporadic fighting on the northern outskirts between rebel militia and forces loyal to exiled President Abedrabbo Mansour Hadi.

A rebel leader, Nabil al-Hashidi, was killed late Wednesday when pro-Hadi fighters stormed his hideout in Aden, tribal sources said, accusing him of "spying" for Iran.

In the rebel-held northern province of Jawf, pro-Hadi tribesmen seized control of Yatamah, a town on the border with Saudi Arabia, tribal sources said.

- Bid to relaunch talks -

The loyalists operated under the cover of coalition air strikes as they later advanced towards a town in the Huthi stronghold province of Saada, the sources said.

These advances come as the pro-Hadi forces chief-of-staff, General Mohammed Ali al-Maqdishi, arrived in the Ramlat al-Sabiin area near the Saudi border to inspect his troops, tribal sources said.

The Saudi-led coalition has waged an air campaign against the Huthis since March 26 in an effort to restore the authority of Hadi, who has fled to Riyadh with members of his government.

A United Nations conference to relaunch political talks on Yemen will open in Geneva next week, a UN spokesman said Wednesday, despite uncertainty over who will attend.

UN chief Ban Ki-moon said the May 28 meeting was to "restore momentum towards a Yemeni-led political transition process" after weeks of conflict that have left 1,850 dead.

Huthi supporter Tehran on Thursday said it backed efforts to relaunch a political dialogue, but also warned against outside interference.

"Iran backs initiatives aimed at bringing Yemeni political groups around the negotiating table," Foreign Minister Mohammad Javad Zarif said as he received the United Nations special envoy to Yemen, Ismail Ould Cheikh Ahmed.

However, Zarif insisted only Yemen's political groups should attend, and that no representatives from "any other country should be present at the dialogue", Iran's Fars news agency reported.

Yemeni Foreign Minister Riyadh Yassin has said he would not go to Geneva unless the Huthis withdrew from at least part of territory they have seized in line with a UN Security Council resolution.