Ukrainian President Petro Poroshenko used his speech at the U.N. General Assembly on Tuesday to rail against Russian aggression, urging the world not to believe "conciliatory" statements from his counterpart Vladimir Putin.

The Russian leader called Monday for a broad U.N.-backed coalition to fight the Islamic State group as he seeks to muscle his way back onto the world stage after months of isolation over Ukraine.

Moscow on Tuesday slammed the holding of a U.S.-led counter-terrorism summit at the United Nations, calling it disrespectful.

On Tuesday, President Barack Obama sat down with more than 100 leaders at the U.N. to push ahead with a U.S.-led campaign against the Islamic State group.

U.S. President Barack Obama said Tuesday that defeating the Islamic State group in Syria will only be possible if Bashar Assad leaves power, a day after a clash with Russia over the Syrian president's fate.

"In Syria (...) defeating ISIL requires, I believe, a new leader," Obama told a counter-terrorism summit of some 100 leaders, held on the sidelines of the U.N. General Assembly.

President Barack Obama met his Cuban counterpart Raul Castro on Tuesday at the United Nations -- all smiles after both renewed their calls for an end to the U.S. trade embargo against Havana.

The leaders of the former Cold War rivals shook hands at the start of what was their second meeting, after an historic encounter in April at the Summit of the Americas in Panama.

An ultraconservative Iranian lawmaker hit out Tuesday at reports Foreign Minister Mohammad Javad Zarif shook hands with U.S. President Barack Obama at the U.N. General Assembly, branding it as un-revolutionary.

The remarks came after Iran's semi-official ISNA news agency and international media outlets documented the impromptu encounter in New York on Monday.

Moscow said on Tuesday that Russia and the United States intended to build upon a key meeting between Vladimir Putin and Barack Obama and look for ways to fight the Islamic State group.

The Russian president stole the show at the U.N. General Assembly on Monday, calling for a broad U.N.-backed coalition to fight Islamic State jihadists.

Russian President Vladimir Putin and his U.S. counterpart Barack Obama met Monday on the crisis in Syria but failed to resolve their dispute over the future role of Bashar Assad.

In dueling speeches before the U.N. General Assembly, Obama branded the Syrian leader a child-killing tyrant while Putin said the world should support Assad against the Islamic State group.

President Barack Obama on Monday called for ending the decades-old U.S. embargo on Cuba, in his address to the U.N. General Assembly.

Obama said he was confident that the U.S. Congress will "inevitably lift an embargo that should not be in place anymore," drawing applause from the 193-nation assembly.

U.S. President Barack Obama insisted Monday that the sanctions Western powers imposed on Moscow in the wake of Russia's intervention in Ukraine were meant to protect Kiev's sovereignty not trigger conflict with Moscow.

"We cannot stand by when the sovereignty and territorial integrity of a nation is flagrantly violated," he said, addressing the United Nations General Assembly.

U.S. President Barack Obama on Monday took a swipe at Russia and Iran for backing what he called "tyrants" like Syria's Bashar Assad but declared in his address to the United Nations that he was ready to work with them to end the conflict.

Obama took the podium at the U.N. General Assembly ahead of President Vladimir Putin and Iranian leader Hassan Rouhani, with the spotlight firmly on ending the carnage in Syria.