UNITED NATIONS, United States -- A United Nations meeting on Ukraine Wednesday heard that a full-scale Russian invasion of the country would have a devastating global impact that would likely spark a new "refugee crisis."

The United States said a war could displace up to five million people while Ukraine's foreign minister said such a conflict would mark "the end of the world order as we know it."

The dire warnings were made during an annual General Assembly session on "temporarily occupied Ukrainian territories" that has been held at UN headquarters in New York every year since Russia annexed Crimea in 2014.

UN Secretary-General Antonio Guterres warned the body that "our world is facing a moment of peril" over the crisis.

"If the conflict in Ukraine expands, the world could see a scale and severity of need unseen for many years," he said.

"It is time for restraint, reason and de-escalation," Guterres added, stressing there was no room for actions or statements that would "take this dangerous situation over the abyss."

America's ambassador to the UN, Linda Thomas-Greenfield, said an invasion could displace as many as another five million people on top of the three million she said had already been impacted by Russian military action in eastern Ukraine.

"If Russia continues down this path, it could -- according to our estimates – create a new refugee crisis, one of the largest facing the world today," she said.

Thomas-Greenfield added that since Ukraine is one of the world's largest wheat suppliers to the developing world, Russian military operations "could cause a spike in food prices and lead to even more desperate hunger in places like Libya, Yemen, and Lebanon."

"The tidal waves of suffering this war will cause are unthinkable," she said.

Earlier, Ukrainian Foreign Minister Dmytro Kuleba pleaded with the UN to hold Moscow accountable for what he called its attack on "the core principles of international law."

"If Russia does not get a severe, swift and decisive response now, this will mean a total bankruptcy of the international security system and international institutions, which are tasked with maintaining the global security order.

"This is a grim scenario, which will throw us back to the darkest times of the 20th century," he said.

Kuleba called Russian claims that it is acting to prevent planned military operations by Kyiv in Donbas area as "absurd" and called on Russia to withdraw troops from Ukrainian soil.

"We Ukrainians want peace and we want to resolve all issues through diplomacy," he said.

All 193 members of the UN attended the meeting, the vast majority speaking out against Moscow.

Russia's UN ambassador, Vassily Nebenzia, said today's tensions were the result of the 2014 "coup" that ousted pro-Russian, ex-Ukrainian prime minister Viktor Yanukovych.

He said that since then Ukraine's government has been carrying out a "genocide" in Donbas.