Kinshasa - A coalition of opponents of DRC President Joseph Kabila announced on Sunday former regional governor Moise Katumbi as their "joint opposition candidate" for presidential elections due before the end of the year.Democratic Republic of Congo authorities are under pressure from the international community to hold the polls as planned in November before Kabila's second - and constitutionally last - mandate ends.Last month police in the southeast of the country fired tear gas to break up a demonstration by 5 000 people in the latest unrest triggered by fears that Kabila plans to extend his rule into a third term.Katumbi, a former regional governor in southeastern Katanga, has called for "a credible presidential election to be held in November 2016, which will end [Kabila's] second term in strict respect of the constitution".On Sunday more than 1 000 supporters chanted Katumbi's name as he was declared the candidate of the newly-formed Alternation for the Republic (AR), which groups 16 small parties."We have decided [to present Katumbi] as joint candidate for the presidential election," said Delly Sessanga, the group's co-ordinator."The designation [of Katumbi] is a decisive step... to guarantee democratic alternation," he added.The country has been in crisis since Kabila's re-election in late 2011 in polls marred by irregularities and massive fraud. His second term expires in December and the constitution bars him from standing again.Katumbi, who went over to the opposition in September after resigning as governor and quitting the president's party, is a major figure in the country's politics.Popular and charismatic, the 51-year-old wealthy businessman is also head of the prestigious Tout-Puissant Mazembe football club, three-time winner of the African Champions League.Another opposition coalition, comprising seven parties which broke away from the majority in September, had already called in March for Katumbi to stand for president.Katumbi himself has not officially confirmed his candidacy.DR Congo's political climate has grown increasingly tense, as the likelihood of presidential polls being held before the end of the year weakens with every passing week.Kabila assumed power after his father, president Laurent Kabila, was assassinated in 2001. He took up his first elected term in 2006, under a new UN-supervised constitution which provided for two five-year mandates in the vast nation of some 81 million people.