BEIJING, Sept. 22 (Xinhua) -- Global leaders have called for efforts to address global challenges by upholding multilateralism and supporting the United Nations (UN), as a high-level meeting to commemorate the 75th anniversary of the UN was held Monday.

Chinese President Xi Jinping on Monday made four proposals on the development of the UN and its role in the post-COVID era.

The UN must stand firm for justice, uphold the rule of law, promote cooperation and focus on real action, said Xi while addressing the UN high-level meeting via video.

"To put into practice the principle of multilateralism, we must act, not just talk," said Xi, stressing that the UN must focus on real action.

Lauding the UN's role in 75 years, Xi said the 75 years has seen dramatic progress in human society and profound changes in the international situation, and has been a period of rapid development of multilateralism.

South African President Cyril Ramaphosa called on all countries to support the UN to "resolve our global challenges -- be they health emergencies, transnational crime, conflict and war, climate change, migration or natural disasters."

"It is only through multilateralism that common strategies can be forged for the benefit of all," Ramaphosa said in his weekly presidential address on Monday.

"A global problem requires global solutions, so only through multilateralism, international cooperation and global governance, can we mitigate the serious consequences of this pandemic and thus build a better planet," Colombian President Ivan Duque told the high-level meeting.

"Amid these difficult times, we send a message of solidarity to all nations that continue to tackle the impact of the COVID-19 pandemic with so much effort ... Today more than ever, we are all united in the face of the unprecedented challenge before us," he added.

"Multilateralism is not an option but a necessity as we build back better and greener for a more equal, more resilient and more sustainable world," Volkan Bozkir, president of the 75th session of the UN General Assembly, said in his opening remarks at the meeting.

The organization's work is more crucial than ever, especially in the context of the threats posed by the COVID-19 pandemic, and support from the member states is an indispensable part, according to the president of the assembly.

"The United Nations must be at the center of our efforts," Bozkir said.

"We must support the United Nations to evolve into more agile, effective, and accountable organization, so it is fit for purpose and can deliver the future we want," he said.

European Council President Charles Michel said Monday that this world needs multilateralism and a strong and effective UN for all people across the world.

"It is with solemnity that today I renew the vow of multilateralism on behalf of the European Union," Michel said at the high-level meeting.

Since the signing of the UN Charter, each time that cooperation, exchange and tolerance have been put into practice, the conditions of life have improved, he said. "Whereas division, isolation, discrimination and injustice have always been synonyms of regression, conflict and, sooner or later, war."