Wearing his signature army green, Zelenskiy traveled to New York to attend a meeting of the 15-member Security Council in-person for the first time since Russia invaded Ukraine in February 2022. The council has met dozens of times since then but has been unable to take any action as Moscow holds a veto.

"Ukraine exercises its right to self-defense," Zelenskiy said. "Helping Ukraine with weapons in this exercise, by imposing sanctions and exerting comprehensive pressure on the aggressor, as well as voting for relevant resolutions, would mean helping to defend the U.N. Charter."

Ukraine and Western countries have successfully isolated Russia diplomatically at the U.N., where the 193-member General Assembly has overwhelmingly voted several times to condemn the invasion and demand Moscow withdraw its troops.

Their argument has been simple: Russia has violated the 1945 U.N. Charter.

In a bid to shore up that support, Zelenskiy also spoke about an issue important to many U.N. members, particularly developing countries in the Global South - reform of the world body, particularly expansion of the Security Council.

"We should not wait for the aggression to be over. We need to act now. Our aspiration for peace should drive the reform," Zelenskiy said.

Zelenskiy's appearance coincided with a pivotal moment for Ukraine's military campaign to eject Russian forces from Ukraine.

Public enthusiasm for the war effort is waning in many NATO countries, the summer counteroffensive has hit stubborn Russian defenses and soon colder, wetter weather will make many rural roads impassable for heavy vehicles.

'STOP THE WAR'

U.N. Secretary-General Antonio Guterres told the council on Wednesday that Russia's war in Ukraine "is aggravating geopolitical tensions and divisions, threatening regional stability, increasing the nuclear threat, and creating deep fissures in our increasingly multipolar world."

Russia's Foreign Minister Sergei Lavrov and U.S. Secretary of State Antony Blinken were also due to address the council.

Before the meeting started, Russia's U.N. Ambassador Vassily Nebenzia objected to Zelenskiy addressing the council, which is chaired by Albania for September, before the 15 members.

"I want to assure our Russian colleagues and everyone here that this is not a special operation by the Albanian presidency," Albania's Prime Minister Edi Rama told Nebenzia. "There is a solution for this. If you agree, you stop the war and President Zelenskiy will not take the floor."

The Security Council has met dozens of times on Ukraine over the past 19 months but is unable to take any action as Russia is a veto power. Russia has said it is carrying out a "special military operation" in Ukraine.

On Thursday, Zelenskiy heads to Washington to meet with U.S. President Joe Biden, members of Congress and military officials to shore up support in Ukraine's most important ally.

While a majority in Congress still support supplying military aid to Ukraine, skeptical voices among Republicans are growing louder as the war's cost rises. House of Representatives Speaker Kevin McCarthy, the leading Republican in Washington, has questioned whether the United States should keep sending billions of dollars in weaponry to Ukraine.

Biden plans to announce a new military aid package during Zelenskiy's visit. In a speech to the U.N. General Assembly on Tuesday, Biden appealed to world leaders to stand with Ukraine against Russia, saying that only Moscow has the power to end the war.