Exiled Yemeni President Abd Rabbuh Mansour Hadi on Monday appointed a new governor of the war-torn country’s southern Aden province, as the death toll from a Houthi militia attack against a nearby town reached nearly 100, predominately civilians.

The appointment comes as pro-government forces, who have made advances against the Houthis in the southern port city in recent days, are reportedly battling to take the last district held by the group.

The Houthi militiamen and their allies started shelling the town of Dar Saad on Sunday, after losing control of some of Aden’s neighbourhoods.

The shelling killed nearly 100 people and left about 200 people wounded, said Hassan Boucenine of the Geneva-based Medicins Sans Frontieres

Of the victims, 80 per cent are civilians, including many pregnant women, elderly and children, he added.

"Yesterday was the worst day in Aden since (the Saudi-led coalition campaign) started in March," Boucenine told The Associated Press, adding that he fears "attacks on civilians will continue."

Fighters from the pro-government Popular Resistance "have regained control of most of Al-Tawahi district," including the presidential residence, said spokesman Ali al-Ahmadi.

The southern fighters have also pushed Houthis and forces allied to former president Ali Abdullah Saleh out of the region's military headquarters and the naval base, Ahmadi told AFP. Al-Maashiq presidential palace in the downtown district of Crater remains in Houthi control.

Forty Houthis have been taken prisoner. Of the remaining Houthis, some have taken positions on several Aden rooftops, he added.

In a presidential decree issued from Riyadh on Monday, Hadi appointed Nayef al-Bakri, a former deputy governor of the province, to the post of governor, according to Yemen’s official news agency.

Al-Bakri, chairman of the Resistance Council in Aden, the political body overseeing the Popular Resistance, had been one of the government officials who did not flee Aden when it was overrun by the Houthis earlier this year.

On Friday, Khaled Bahah, Yemen’s vice-president and prime minister, declared that Aden had been “liberated” from the Houthis and allied forces loyal to ousted President Ali Abdullah Saleh.

Clashes, however, have remained ongoing on the outskirts of the city, which is considered the country’s commercial and economic capital.

At least 17 Houthis and 11 pro-government fighters have been killed in clashes since Sunday, according to military sources and health officials.

The pro-government push for Aden - dubbed "Operation Golden Arrow" - began last Tuesday, backed by Saudi-led warplanes.

Two ministers from the government in exile in Saudi Arabia returned to Aden at the weekend, touring the devastated city.

Transport Minister Badr Basalmeh told journalists in the city that a technical team had arrived from the United Arab Emirates to repair the control tower and passenger terminal at Aden international airport, which was heavily damaged in clashes before Houthi forces were driven out.

More than 3,200 people, many of them civilians, have been killed in fighting across Yemen since Saudi-led airstrikes began in March, the UN said.