United Nations Secretary-General Antonio Guterres warned leaders on Tuesday that world order is “increasingly chaotic,” trust is at breaking point and shifts in the balance of power may increase the risk of confrontation, though he did not lay blame.

As U.S. President Donald Trump prepared to tout protection of U.S. sovereignty at the annual U.N. gathering of world leaders, Guterres told the 193-member U.N. General Assembly that multilateralism is under fire when it is needed most.

“Individual leaders have the duty to advance the well-being of their people,” Guterres said. “But it runs deeper ... As guardians of the common good, we also have a duty to promote and support a reformed, reinvigorated and strengthened multilateral system.”

He called for a renewed commitment to a rules-based order with the United Nations at its centre and warned against a spreading “politics of pessimism.”

“Those who see their neighbours as dangerous may cause a threat where there was none. Those who close their borders to regular migration only fuel the work of traffickers,” Guterres said. “And those who ignore human rights in combating terrorism tend to breed the very extremism they are trying to end.”

He also urged leaders to tackle climate change with a greater sense of ambition and urgency and said he would hold a summit on the issue in September next year. The Trump administration withdrew from a global accord to reduce emissions last year.

“If we do not change course in the next two years, we risk runaway climate change,” Guterres said.