A visit by the UN’s counterterrorism chief to China’s western Xinjiang region has sparked outrage from human rights groups who say it legitimises Beijing’s treatment of more than one million Uighur Muslims detained there.

Beijing has long argued that its use of detention centres in the region is justified in order to help stamp out extremism and give people new skills. But the complexes have seen China condemned internationally, with accusations of widespread abuses, disappearances and arbitrary detentions targeting the Muslim community.

The UN’s high commissioner for human rights, Michelle Bachelet, requested permission to visit Xinjiang and assess the situation in December. On Thursday, China’s envoy to the UN in Geneva said they were yet “to define a time which is convenient to both sides”.

Yet it seems a convenient time was found for a trip by Vladimir Voronkov, a former Russian diplomat and the UN’s undersecretary general for counterterrorism. His visit, first reported by Foreign Policy magazine and later confirmed by a UN spokesperson, sees him become the highest-level UN official to visit the restive region.

Details of Mr Voronkov’s itinerary were not immediately revealed, but UN spokesperson Farhan Haq did issue a statement saying the UN’s counterterrorism office always worked to ensure that measures used to fight terror respected human rights.

Louis Charbonneau, the UN director for Human Rights Watch, told Foreign Policy that Mr Voronkov’s visit was “handing China a propaganda victory”.

“The UN allowing its counterterrorism chief to go to Xinjiang risks confirming China’s false narrative that this is a counterterrorism issue, not a question of massive human rights abuses,” he said.

And Prince Zeid Ra’ad Al Hussein of Jordan, the former UN human rights commissioner who clashed with China on a number of occasions, said a simple government-controlled visit to Xinjiang would be “quite useless, rais[ing] dramatically the possibility of staging and whitewash”.

The UN formally raised concerns over the human rights situation in Xinjiang during a visit by secretary general Antonio Guterres to China in May. At the request of some western countries, he told China’s prime minister that rights in Xinjiang “must be respected”.

China insisted on Thursday that an invitation to rights chief Ms Bachelet “is always there”, with envoy Chen Xu praising her approach of “dialogue and cooperation” and contrasting it to that of her predecessor Prince Zeid.