US President Barack Obama and UN Secretary General Ban Ki-moon called Tuesday on the global community to do more to address international crises, from the war in Syria and the refugee crisis to North Korea's nuclear programme.
For both, it would be their final addresses to the UN General Assembly.
Obama, whose term in office ends in January, defended progress brought by global integration and denounced the isolationist desire to build walls and retreat from the world stage.
Growing economic inequality has given rise to an increase of ethnic and religious sectarianism as well as aggressive nationalism and populism, he said.
"Today a nation ringed by walls would only imprison itself," Obama said, in a nod to calls by Republican presidential candidate Donald Trump to build a wall along the southern US border with Mexico.
Obama also called for greater action to help refugees fleeing conflict in Syria and elsewhere.
"We have to do more and open our hearts to refugees who are desperate for a home," he said, appealing to nations to follow through with aid pledges despite the difficult politics of the issue.
UN Secretary General Ban, addressing the assembly for the last time of his 10-year tenure, delivered an unusually strong address reprimanding world leaders for their failures over Syria and the Middle East, while also warning against the spread of xenophobia.
He singled out the Syrian government as the main culprit for the bulk of violence inflicted on the Syrian people, citing the country's continued use of barrel bombs and torture.
"Powerful patrons that keep feeding the war machine also have blood on their hands," said Ban, noting that representatives of those governments were sitting in the hall.
Turning to the breakdown of peace talks in the Middle East, Ban said the prospects of a two-state solution between Israel and the Palestinian Territories were "being lowered by the day," warning that replacing it with a "one-state construct would spell doom."
"This is madness," Ban said.
He also warned of the hatred refugees and migrants often experience, noting that Muslims particularly face "stereotyping and suspicion that have haunting echoes of the dark past."
"I say to political leaders and candidates: do not engage in the cynical and dangerous political math that says you add votes by dividing people and multiplying fear," Ban said.
The refugee issue has already been a major topic at the UN this week. The 193 UN member states adopted a non-binding political declaration Monday, committing to better manage the flow of migrants and refugees by ensuring human rights, protecting vulnerable groups and enhancing global responsibility-sharing.
An estimated 65 million people have been forcibly displaced from their homes, including more than 21 million people who have fled across international borders.
Obama convened the refugee summit later Tuesday where he secured agreements to fund food aid and to double refugee resettlement in third countries each year.
Following the breakdown of a US-Russia brokered ceasefire deal in Syria just a day before, French President Francois Hollande told the assembly that the UN Security Council must come together and find a solution to the Syrian crisis.
"It should not be a theatre for fools - in other words, a place where each evades their responsibility and where some impede the work of the Security Council," Hollande said.
"The Syrian tragedy will be seen by history as a disgrace to the international community if we do not end it quickly."
Obama also offered tough words for Russia's support of the Syrian regime, as well as for Moscow's incursion in Ukraine.
"We see Russia attempting to recover lost glory through force," Obama said.
Without specifically mentioning Russian President Vladimir Putin or other world leaders, he denounced "strongmen" who seek to maintain power by either perpetual political crackdowns at home or creating conflicts abroad.
The US leader also called for global action against North Korea's nuclear programme in the wake of recent nuclear tests by the reclusive government, describing the country as a "wasteland."