Aden (AFP) - At least 55 people, including 14 civilians, have been killed in two days of fighting between pro-government forces and Shiite Huthi rebels in Yemen, officials said Sunday.

The clashes came as UN special envoy Ismail Ould Cheikh Ahmed was in the rebel-held capital Sanaa for meetings with the Huthis aimed at restarting peace talks with the internationally recognised government.

Since Saturday, fighting has raged in the outskirts of third city Taez as rebels try to retake positions lost in recent weeks to loyalists, military sources said.

Pro-government forces backed by a Saudi-led coalition managed earlier this month to break a months-long rebel siege of the southwestern city.

"At least 26 people, including 14 civilians, have been killed in 24 hours" in rebel shelling of residential neighbourhoods and loyalist positions, a local official told AFP.

Taez lies between Sanaa, which rebels overran in September 2014, and the port city of Aden -- the temporary base of the government of President Abedrabbo Mansour Hadi.

On another front, six pro-Hadi fighters and seven rebels were killed Saturday in clashes in the southern province of Shabwa, where loyalists advanced in the oil-rich area of Baihan, another military source said.

In the neighbouring province of Marib, pro-Hadi forces on Saturday captured the Harib area, the military source said, adding that 13 rebels and three loyalists were killed in the fighting.

As well as the 55 dead in fighting between pro-government forces and rebels, two loyalists were killed late Saturday in an ambush that targeted a convoy heading from Taez to Aden, a military source said, accusing the Islamic State group of being behind the attack.

IS and Al-Qaeda militants have gained ground in southern Yemen since the coalition launched air strikes in the country in March last year, after the rebels closed in on Hadi in Aden, forcing him to flee to Riyadh.

Loyalists last summer recaptured Aden and four other southern provinces including Shabwa, but its northern area of Baihan remained in rebels hands.

The World Health Organisation says fighting in Yemen has killed more than 6,200 people over the past year and the United Nations has warned of an unfolding humanitarian catastrophe.