Kinshasa - A pro-democracy movement has called for the release of five of its activists detained in the Democratic Republic of Congo, saying it fears they could be tortured.The activists from the Filimbi movement, whose name means "whistle" in Swahili, are accused of "insulting the head of state and inciting a revolt", according to their lawyer, Chris-Sam Kabeya.Four of the activists were arrested in Kinshasa on December 30 while trying to organise a protest march against the 17-year rule of President Joseph Kabila for the next day, New Year's Eve.All were "detained in total secret since January 1, 2018... at the National Intelligence Agency (ANR) where they would be tortured," according to a statement from the pro-democracy movement received by AFP on Saturday.The fifth activist was held a week earlier in the eastern town of Kindu by the military intelligence service where he "was tortured", said the statement."To this day, it is difficult for us to confirm that they are still alive," it added."We condemn with the utmost energy these barbaric acts and demand the unconditional release of our activists."The New Year's Eve anti-Kabila protest descended into violence after the authorities cracked down on demonstrators.Protest organisers said 12 people were killed, while the United Nations gave a toll of at least five dead - a figure that it said could be "far higher," as its investigators had been barred from visiting morgues, hospitals and detention centres.An AFP reporter at a demonstration in the central city of Kananga saw a man shot in the chest by soldiers who opened fire on worshippers.Members of the Filimbi movement have repeatedly been arrested by the authorities in DR Congo, often for speaking out against Kabila. The new arrests are another sign of rising tensions in the vast central African nation, where the opposition does not want the president's grip on power to continue.Under a Catholic church-brokered 2016 deal, Kabila was allowed to stay in office provided new elections were held in 2017. After months of silence, the authorities said the vote would be held in December 2018 -- a postponement that has angered democracy activists and Western nations.