By Agence France-Presse US President Donald Trump's all-out assault on the United Nations is doing "lasting damage" to international cooperation as the world faces a range of "existential threats", a former WHO chief warned Friday. Gro Harlem Brundtland, a former Norwegian prime minister who served as head of the UN health agency from 1998 to 2003, said she was deeply concerned about concerted efforts by populist leaders in the US and elsewhere to tear down vital multilateral systems. She pointed to Trump's recent decision to withdraw the US from the World Health Organization as it attempts to coordinate the response to the global coronavirus pandemic as "perhaps the most astonishingly and transparently counter-productive of all these moves. "You cannot deal with a pandemic or to avoid or prepare against such a terrible situation without very extensive international collaboration," she told a virtual briefing hosted by the UN press association in Geneva. Brundtland, currently a member of The Elders, a group of statespeople co-founded by Kofi Annan to advise on global issues, slammed "wilful destructiveness of certain national leaders" who appeared determined to tear down UN agencies and other international institutions at a time when they are sorely needed. "If we have learned anything from the last few months it is that existential threats like pandemics, climate change and nuclear weapons can only be countered by collective and concerted efforts," she said. In addition to announcing that the US, traditionally WHO's largest donor, was leaving the UN health body, Trump has attacked a range of other international institutions since taking power in 2017. He pulled the US out of the Paris climate accords, quit the UN Human Rights Council, basically shut down the World Trade Organization's appeals body by blocking the appointment of judges, and has begun withdrawing from several major disarmament treaties. - 'Alarming' - "It is an especially sad irony that this assault on multilateralism is being led by the country that played the single biggest role in the establishment and maintenance of the multilateral system after 1945," Brundtland said. Under Trump, "the US government has sought to undermine and dismantle some of the crowning achievements of multilateralism," she said. "To my great regret, the current US administration has done lasting damage to the UN system and the broader principles of multilateralism since 2017." The pandemic has brought the dangers posed by populist, nationalist and isolationist leaders in a range of countries like Brazil, Hungary, Israel and the Philippines into stark relief, she said. "It is alarming that some populist leaders have used the crisis as a means of subverting democracy, human rights and accountability," she said. She also expressed outrage at leaders who have chosen to ignore scientific opinion in a bid to score political points, despite in some cases soaring numbers of cases and deaths in their countries. "My only hope is that public opinion will change and that in countries like these, the demagoguery and the way they place and describe problems will not be anymore listened to," she said.