A Cambodian opposition leader has been sentenced to five months in prison as political tensions continue over challenges to the autocratic rule of the prime minister, Hun Sen. Kem Sokha, the vice-president of the Cambodia National Rescue party (CNRP), was sentenced after a trial lasting several hours. His defence lawyer, Sam Sokong, said Kem would appeal against the verdict. "The trial conducted today did not comply with procedures," he said. Kem, who was not in court, was convicted of twice ignoring summons to answer questions relating to a case involving his alleged mistress. He refused, saying the legal moves were part of attempts by the ruling Cambodian People's party (CPP) to cripple the opposition. Riot police were outside the court and nearly 1,000 opposition supporters gathered in front of the CNRP headquarters, with riot police watching them from about 500 metres (1,640ft) away. There were no reports of violence. The CNRP politician Ou Chanrith said the party was not surprised by the verdict and urged supporters to continue challenging government suppression. The case is one of several hanging over opposition leaders in what is generally seen as an attempt to disrupt their organising efforts before local elections next June. The next general election is not until the middle of 2018, but being in power at a local level is an advantage when national polls are held. Before the verdict, Kem appeared before his supporters and accused the government of using the courts to prevent him from speaking out and taking part in the elections. A statement issued this week by the UN high commissioner for human rights expressed concern "about the escalating atmosphere of intimidation of opposition politicians, their supporters, civil society and peaceful demonstrators in Cambodia". It noted "a host of legal charges" faced by Kem and 29 opposition supporters. Advertisement The statement said 14 of them had been given long prison sentences, despite serious concerns about the fairness of the proceedings. "We urge the authorities to adhere strictly to international fair trial standards during the criminal proceedings," it said. The CNRP president, Sam Rainsy, did not return from a trip abroad last November after a previous conviction for defamation was reinstated and his parliamentary immunity was removed by the government's legislative majority. It had been generally assumed that the conviction, which carried a two-year prison sentence, had been lifted by a pardon in 2013 that allowed Sam to return from exile. He also faces a series of separate charges that could see him imprisoned for 17 years. Activists and non-governmental organisations, which are generally critical of the government, have been subjected to similar legal pressures. There has also been violence against two opposition politicians, who were beaten up by a pro-government mob last year, and the murder of the prominent social critic Kem Ley in July, allegedly by a man he owed money. The opposition, which has strong support in the capital, Phnom Penh, has called on its followers to protest. But recent attempts at street demonstrations, which have previously been effective, were thwarted by a government show of force. Hun has been Cambodia's leader since 1985, but it appeared that his grip on power was waning when the CNRP won 55 seats in the national assembly and left his CPP with 68 in the 2013 general election. The opposition claimed that they had been cheated and boycotted parliament. Seeking to legitimise his continued rule, Hun reached a truce with the CNRP in 2014, making some minor concessions over electoral and parliamentary procedures. But relations between the government and the opposition deteriorated last year after the latter accused neighbouring Vietnam, with which Hun's government maintains good relations, of land encroachment. The move proved politically popular and the government reacted by stepping up intimidation of the CNRP through the courts. In the past, the CPP was often accused of using violence or the threat of violence against opponents, but the strategy appears to have changed in recent years. UPDATE: On 27 March 2018, Cambodia's Appeals Court upheld the continued detention without bail of opposition leader Kem Sokha, as Prime Minister Hun Sen boasted that he personally ordered the arrest last year that has earned Phnom Penh international condemnation and cuts in aid from donor counties.