* Each side accuses other of violating ceasefire
* Prisoner swap blocked by angry tribesmen
* Almost 6,000 killed in nine months of civil war (Recasts with ceasefire in danger of collapse)
By Mohammed Mukhashaf
ADEN, Dec 16 (Reuters) - A ceasefire between Yemen's Houthi group and a Saudi-led alliance was in danger of collapse on Wednesday, each side accusing the other of violating the truce, as peace talks went into a second day in Switzerland.
Brigadier General Ahmed al-Assiri of the Saudi coalition said the Iran-allied Houthis had repeatedly broken the ceasefire supposed to begin at midday on Tuesday and that his forces were responding.
The truce was intended to last seven days and coincide with the peace talks to try to end a nine-month-old civil war between the Houthis based in Yemen's north and Saudi-backed southern and eastern fighters loyal to President Abd-Rabbu Mansour Hadi.
Nearly 6,000 people have been killed in the fighting and millions displaced.
"The number of violations is around 150 and this does not show honest intentions," Assiri told al-Ekhbariya television.
"We urge the United Nations to clarify to the Houthis that there will be no patience towards these practices and the truce could collapse at any moment," he said, adding Saudi Arabia would not tolerate any attacks on its border from Yemen.
The remarks came after a spokesman for Yemeni government forces loyal to former President Ali Abdullah Saleh, an ally of the Houthis, accused the Saudi-led coalition of a "serious escalation by land, sea and air", according to the Houthi-controlled Saba news agency.
The spokesman, Brigadier General Sharaf Luqman, said strikes from the sea were taking place on the Red Sea port city of Hodaida, ground forces had attacked Taiz city in southwest Yemen and air strikes by the Arab coalition had not stopped.
"We will respond strongly towards the breaches that are taking place by the alliance and their mercenaries," the Houthi-run Saba news agency (www.sabanews.net) quoted Luqman as saying.
"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 Taiz said there was an air strike there after Houthi forces launched rockets on the area. Saudi state news agency SPA said the Houthis had killed one of its officers in a border area after the ceasefire was supposed to begin.
PRISONER SWAP DELAYED
Local tribesmen held up a prisoner swap between the Houthis and southern fighters, local officials said.
Armed tribesmen from al-Baydah province in central Yemen blocked roads leading to the exchange venue, demanding that their relatives held by the Houthis also be included in the swap.
Officials from both sides had earlier said 360 Houthis and 265 southern Yemenis were on their way to be exchanged on the border between Yafe and al-Bayda provinces at midday.
Residents said mediators were trying to persuade the al-Baydah tribesmen to allow the swap to proceed.
The prisoner swap, brokered by Yemeni tribal chiefs, had been one of the most positive signs yet in the conflict.
Most of the Houthi prisoners are fighters aged between 13 and 16, captured when the Southern Resistance retook the southern port city of Aden in July.
Little official news has emerged from the Swiss talks organised by the United Nations, but delegates reached through social media sounded positive about the first two days of negotiations. (Additional reporting by Ali Abdelatti and Omar Fahmy in Cairo; Writing by Maha El Dahan and Sami Aboudi; Editing by Andrew Roche)
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