Kinshasa - The Democratic Republic of Congo refused on Tuesday to renew the visa of a senior Human Rights Watch (HRW) researcher, who was to leave the troubled African country shortly.Kinshasa did not give a reason for the decision to effectively expel Ida Sawyer, who has worked for the US rights group in DR Congo since 2008.The government's immigration service "did not want to renew the visa ... That is all," government spokesperson Lambert Mende told AFP."Some governments never give justifications" when they refuse visas. "We will not justify ourselves. It's the principle of reciprocity between states," he added.Sawyer, who has been based in DR Congo since January 2008 - first in Goma, capital of the eastern North Kivu province, then in Kinshasa since 2011 - was due to leave Kinshasa later on Tuesday.She has carried out research across the country as well as in parts of neighbouring countries occupied by Lord's Resistance Army (LRA) rebels. Her work has served as the basis for numerous HRW reports, the group said on its website.The local office of HRW, which regularly condemns violations of human rights in the DRC, declined to comment immediately on the visa decision.Political tensions have risen as President Joseph Kabila nears the end of his term in office on December 20. The constitution bars him from standing for re-election.Kabila has been in office since 2001. Opposition leaders suspect he is manoeuvring to cling to power, possibly by delaying presidential polls which appear unlikely to take place as anticipated at the end of the year.