UN chief Ban Ki-moon came out all diplomatic and political guns blazing to defend protesters in the Arab world and civilians in Ivory Coast, but on a new wave of arrests in China: silence. The former South Korean foreign minister has, through his first term as UN secretary general, stressed the role of \"quiet diplomacy\" for some prickly cases. But the disappearance of dozens of artists, intellectuals and dissidents in China in recent weeks comes as Ban prepares to announce whether he will seek another five years. Even if there is no clear rival for the post, Ban knows that he must have the support of the five permanent members of the UN Security Council -- China, along with Britain, France, Russia and the United States. The UN leader took a tough line on Ivory Coast, where strongman Laurent Gbagbo was captured April 11, and in Libya, where he says that the UN resolution allowing military action extended the frontier of humanitarian law to help civilians. But questioned twice at briefings in recent days about Ban\'s position on the arrest of artist Ai Weiwei and dozens of other opposing voices in China, deputy UN spokesman Farhan Haq said: \"I\'ll have to get back to you on that.\" Rights groups previously criticized Ban for failing to raise the case of jailed Nobel Peace prize laureate Liu Xiaobo when he met China\'s President Hu Jintao in November. Ban insisted that he raised the case with \"other\" Chinese leaders. The same rights groups say China\'s fears that the popular uprisings in the Arab world could spread are behind its move to detain or put under house arrest at least 54 dissident voices. The European Union and United States have expressed concern about the detention of Ai, an acclaimed artist and critic of the communist government. Most international leaders have remained silent on the China arrests however, fearing Beijing\'s wrath. The main UN comment has come from the High Commissioner for Human Rights Navi Pillay and a working group on enforced or involuntary disappearances which last week called the Chinese arrests \"the continuation of a disturbing trend in the suppression of dissidents.\" Human Rights Watch has demanded that Ban speak out, even if he is \"under pressure\" from a key Security Council member. \"If the secretary general\'s new assertiveness on human rights is to be meaningful, it has to extend to the appalling spike in repression in China,\" said Philippe Bolopion, HRW\'s UN specialist. \"The very right to peaceful dissent the secretary general has been championing in the Middle East and North Africa is under attack for many Chinese. Quiet diplomacy having failed with Beijing, it\'s time for the secretary general to speak out on this issue.\" Christopher Walker, director of studies at the Freedom House think tank, said: \"The absence of a consistent and vocal response to this repression in China is troubling\" and could be taken by China as acceptance of what it does. \"It\'s very important to be clear, at the sort of arrests and detentions and extra-legal detention that we\'ve seen recently, are vocally responded to.\" A diplomat from a Security Council nation, speaking on condition of anonymity, said \"the secretary general has been clear about the importance of protecting civilians. \"You cannot minimize the question of human rights in China, however, and it is true he could have expressed a view.\"