Yemen's warring parties agreed on Wednesday to exchange hundreds of prisoners in a move aimed at supporting UN-sponsored peace talks which resumed for a second day in Switzerland, as reported fighting and air strikes appeared to violate a ceasefire.

A seven-day truce, timed to coincide with the peace talks, began at mid-day on Tuesday to halt fighting in nine months of civil war between the Iran-allied Houthi movement based in Yemen's north and Saudi-backed southern and eastern fighters loyal to President Abd-Rabbu Mansour Hadi.

The prisoner swap would be one of the most positive signs yet in the civil war, which has killed almost 6,000 people and drawn in foreign powers.

Some 360 members of the Houthi movement held in Aden would be exchanged for 265 southern civilians and fighters, and both groups were en route by bus toward the exchange venue in central Yemen according to officials from the warring sides.

Despite the truce, Saudi-led air strikes hit positions of the Houthi group in two conflict zones on Wednesday, residents and tribal sources said.

"Coalition planes launched an air strike on the positions of the Houthis and Saleh forces in the Najd area of Sirwah district after they repeatedly violated the ceasefire," a tribal source said by telephone from the central province of Mareb.

Residents in the southwestern city of Taiz also reported an air strike there after Houthi forces launched rockets on the area. Saudi state news agency SPA said the Houthis killed one of its officers in a border area after the ceasefire began.

The Saudi-led coalition's spokesman, Brigadier General Ahmed al-Asseri, could not be immediately reached for comment.

Brigadier General Sharaf Luqman, a spokesman for Yemeni forces loyal to former president Ali Abdullah Saleh, who is allied with the Houthis, said a "serious escalation by land, sea and air is taking place by the alliance in various areas," according to the Houthi-controlled Saba news agency.

Luqman said strikes from the sea were taking place on the Red Sea port city of Hodaida, while ground forces carried out attacks on Taiz city in southwestern Yemen and air strikes by the Arab coalition had not stopped.

"We will not stay hand-tied but we will respond strongly towards the breaches that are taking place by the alliance and their mercenaries," Luqman said.

The Hadi-run sabanew.net news agency said five loyalist fighters and three civilians were killed in Houthi shelling in the central city of Taiz shortly after the ceasefire began.

Asseri said earlier the alliance was committed to the ceasefire but was ready to respond to any violation by the Houthis, according to the Saudi al-Riyadh daily.-Reuters