China has rejected a request by the UN High Commissioner for Human Rights, Louise Arbour, to visit Tibet in April, a UN spokesman confirmed Thursday, according to dpa. Spokesman with the High Commissioner's office, OHCHR, Rupert Colville, said: "The High Commissioner had asked to visit but the Chinese authorities had said it would not be convenient at this time." He added: "China said Louise Arbour would be welcome later at a mutually convenient date." The refusal comes as six UN human rights experts from the Working Group on Arbitrary Detention issued a joint statement of concern regarding the ongoing protests and reports of high numbers of arrests in Tibet and surrounding areas in China. The experts urged restraint by all parties. They were concerned by reports of the arrests of more than 570 Tibetan monks on March 28 and 29, including some children. It followed raids by security forces on monasteries in Ngaba County and in Dzoge County in the Tibetan Autonomous Region. The statement said: "The UN experts are deeply concerned by reports of security forces firing on protestors and alleged killings." The experts also called for greater access for journalists and independent observers.