NAIROBI, Nov 27 (Reuters) - A U.N. court on Tuesday dismissed appeals by a former Rwandan colonel convicted of genocide and upheld his 25-year prison sentence. Aloys Simba, 69, was convicted and sentenced in December 2005. "The conviction was upheld, there will be no change in his sentence," said Timothy Gallimore, spokesman for the Tanzania-based International Criminal Tribunal for Rwanda. The ICTR was set up to find and prosecute architects of the 1994 genocide in which Hutu militants killed an estimated 800,000 Tutsis and moderate Hutus in one of the worst bouts of blood-letting in Africa's history. In his appeal, Simba had argued there were errors of fact and procedure, and that some witnesses lacked conviction, Gallimore said. During his trial, prosecutors said Simba was a close friend of assassinated Rwandan President Juvenal Habyarimana whose death triggered the three-month killing spree. Simba was found guilty of supplying guns and grenades to Hutu militia. The ICTR, which has sentenced 29 people and acquitted five since 1997, is under intense pressure to meet a United Nations deadline to wrap up in 2008. Rwanda wants to take on the role of prosecuting suspects after that. (Reporting by Wangui Kanina, editing by Andrwe Cawthorne and Mary Gabriel)