ADEN: Yemeni pro-government forces and rebels completed an exchange of hundreds of detainees Thursday, an official said, amid a shaky ceasefire and as U.N.-sponsored peace talks in Switzerland entered their third day.

"We have successfully completed the process of exchanging the prisoners," said Mokhtar al-Rabbash, a member of the prisoners' affairs committee, which is close to the government.

The swap involved 370 Houthi rebels and 285 pro-government fighters, he said.

It took place in the Yafaa district of the southern province of Lahj, along the border with the central province of Bayda, witnesses said.

The swap was slowed down by concerns over security along the route linking the two points of exchange, Rabbash said.

The International Committee of the Red Cross in Sanaa, which was involved in a previous prisoner swap, said earlier that the organisation was "not aware of such an exchange".

Little information has emerged from the open-ended talks in Switzerland aimed at ending Yemen's devastating conflict.

A fragile ceasefire declared by forces loyal to embattled President Abedrabbo Mansour Hadi, which began Tuesday, remained shaky with reports of sporadic violations on the ground.

The Saudi-led coalition supporting Hadi accused Huthi Shiite rebels of flouting the ceasefire immediately, and acknowledged that it had "responded to these violations".

Heavy clashes erupted overnight Wednesday in Marib province, east of rebel-held Sanaa, between pro-government Popular Resistance fighters and the insurgents, witnesses said.

The Houthis and allied renegade troops loyal to former president Ali Abdullah Saleh were also accused of bombing areas controlled by pro-Hadi forces in the flash-point city of Taez.

More than 5,800 people have been killed in the country -- about half of them civilians -- and more than 27,000 wounded since March, according to the U.N..