UNITED NATIONS - UN Secretary-General Antonio Guterres warned on Tuesday that multilateralism is under fire at a time when the world needs it most.

"Our world is suffering from a bad case of 'trust deficit disorder'," Guterres told world leaders attending this year's high-level General Debate of the UN General Assembly. "And multilateralism is under fire precisely when we need it most."

Trust is at a breaking point - trust in national institutions, trust among states, trust in the rules-based global order, he said. "Within countries, people are losing faith in political establishments, polarization is on the rise and populism is on the march."

Among countries, cooperation is less certain and more difficult. And divisions in the Security Council are stark. Trust in global governance is also fragile, as 21st-century challenges outpace 20th-century institutions and mindsets, said the UN chief.

"We have never had a true system of global governance, and much less a fully democratic one," said Guterres in his "state-of-the-world" speech that preceded those of world leaders at the General Debate.

"Still, across many decades, we established solid foundations for international cooperation. We came together as united nations to build institutions, norms and rules to advance our shared interests. We raised standards of living for millions. We forged peace in troubled lands and, indeed, we avoided a third world war. But none of this can be taken for granted."

The world is becoming multipolar. But multipolarity will not, in itself, guarantee peace or solve global problems, he warned.

A century ago, Europe was multipolar. A balance of power was deemed sufficient to keep rivals in check. It was not. Without strong multilateral frameworks for Europe-wide cooperation and problem-solving, the result was a grievous world war.

Today, with shifts in the balance of power, the risk of confrontation may increase, warned Guterres.

But conflict is never inevitable, he said. "Indeed, with leadership committed to strategic cooperation and to managing competing interests, we can avoid war and steer the world onto a safer path."

Today, the world order is increasingly chaotic. Power relations are less clear. Universal values are being eroded. Democratic principles are under siege, and the rule of law is being undermined. Impunity is on the rise, as leaders and states push the boundaries, both at home and in the international arena, he said.

The threat of terror looms, fed by the root causes of radicalization and violent extremism. And terrorism is ever more interlinked with international organized crime and the trafficking of people, drugs, arms and corruption, he said.

The nuclear peril has not eased, with non-proliferation at serious risk. Nuclear-armed states are modernizing their arsenals. A new arms race could be triggered, and the threshold for their use lowered, said the UN chief.

"We have seen outrageous uses of chemical weapons, in full impunity despite their ban, and protections against dangerous biological weapons are weak."

He said that inequality is undermining faith in the social contract and is a clear obstacle to the achievement of the Sustainable Development Goals.

Tensions over trade are on the rise, he noted.

Migrants and refugees continue to face discrimination and demagoguery in the context of clearly insufficient international cooperation. And in this year marking the 70th anniversary of the Universal Declaration of Human Rights, the human rights agenda is losing ground and authoritarianism is on the rise.

"There is outrage at our inability to end the wars in Syria, Yemen and elsewhere," he said. "The Rohingya people remain exiled, traumatized and in misery, still yearning for safety and justice. Palestinians and Israelis are still locked in endless conflict, with the two-state solution more and more distant."

On the positive side, there is momentum for peace in the Horn of Africa as a result of detente between Ethiopia and Eritrea; in South Sudan; and in Colombia.

The Singapore summit between US President Donald Trump and the top leader of the Democratic People's Republic of Korea and a recent summit meeting in Pyongyang between the two Koreas have helped de-escalate the tensions on the Korean Peninsula, he noted.

Hundreds of millions of people have been lifted out of extreme poverty across the world over the past three decades, and drive for gender equality is gaining ground, he observed. "Despite the chaos and confusion in our world, I see winds of hope blowing around the globe."

He called for action by world leaders.

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

"We need commitments to a rules-based order, with the United Nations at its center and with the different institutions and treaties that bring the (UN) Charter to life. And we need to show the added value of international cooperation by delivering peace, defending human rights and driving economic and social progress for women and men everywhere."

In the face of massive, existential threats to people and the planet - but equally at a time of compelling opportunities for shared prosperity - there is no way forward but collective, common-sense action for the common good, he said.

As the politics of pessimism spreads, the world must guard against self-fulfilling prophecies, he warned. Those who see their neighbors as dangerous may cause a threat where there was none. Those who close their borders to regular migration only fuel the work of traffickers. And those who ignore human rights in combating terrorism tend to breed the very extremism they are trying to end.

"Our future rests on solidarity. We must repair broken trust. We must reinvigorate our multilateral project," said Guterres.