Government troops in South Sudan were on Monday advancing on Bor, the last state capital still in rebel hands, as ceasefire talks in neighbouring Ethiopia were called off for a day.The latest snag for the peace talks between South Sudan’s government and rebels came when discussions were moved to a new venue, a nightclub in the Ethiopian capital’s top hotel, sparking off complaints from some delegates.Negotiations are expected to resume on Tuesday, though the venue is yet to be confirmed.Back in South Sudan, troops loyal to Dr. Riek Machar  were still trying to take back Bor, the capital of Jonglei state that has already changed hands three times since fighting broke out one month ago."Bor is still in the hands of the rebels but our forces are moving towards it,” army spokesman Colonel Philip Aguer, said.Bor lies some 200 kilometres (125 miles) north of Juba.The fighting, which started on December 15, pits forces loyal to President Salva Kiir against a loose coalition of army defectors and ethnic militia nominally headed by Machar, a former vice-president and seasoned guerrilla fighter.Mediators from the East African regional bloc IGAD are trying to negotiate a truce after a month of fierce fighting in the world’s newest nation that has left thousands dead and forced an estimated 400,000 people to flee their homes.Delegates complained on Monday that a new venue for the talks, the Gaslight nightclub, was too noisy, too spacious and poorly-lit, even though the talks were taking place outside the nightclub’s usual opening hours, sources in Addis Ababa said.A more serious sticking point in the peace talks has been the release of 11 senior politicians, who Kiir accuses of staging a coup. The opposition has insisted on their release, while the government says they must face a legal process."We continue to put pressure on both sides  to sign the agreement and also on the government to agree to the release of the 11 detainees,” US envoy Donald Booth, told journalists on Sunday.Government troops recaptured the key north oil city of Bentiu last week, but have since grappled with rebel fighters closing in to the capital Juba, with new clashes reportedly taking place just 20 kilometres from the capital."Salva Kiir sent a strong force to attack our position. The attackers were destroyed in a two-hour fight,” rebel spokesman Lul Ruai Koang, said in a statement.‘Evidence of atrocities’Aguer confirmed that clashes had taken place, but there was no immediate confirmation of who had an upper hand.The rebel force in the region is commanded by Alfred Ladu Gore, a respected fighter from the Juba region and one of several opposition figures on the government wanted list.The rebels also claim they are close to retaking Malakal, the capital of the biggest oil-producing state Upper Nile.An AFP photographer who was in Malakal on Sunday said the town was calm but that the remaining residents were huddled in the town centre, too scared to return to their looted homes.Humanitarian agencies trying to help the displaced have complained of obstruction, including the killing of aid workers, the confiscating of vehicles and equipment and the looting of their premises.Meanwhile, the Satellite Sentinel Project, co-founded by Hollywood star George Clooney, released images detailing what it said was a "deliberate” destruction of homes and markets in two towns, Mayom in oil-rich Unity and Bor."Evidence of atrocities against civilians should be collected and used for future prosecution for war crimes. There will be no peace if massive human rights abuses can be committed with no accountability,” Clooney said in a statement.