In his speech on Monday morning, Obama opened by calling for recognition of what the UN had achieved and called for international cooperation to solve problems.

He addressed the responsibilities big nations to preserve international order, and criticized both Russia's policies towards Ukraine and Chinese territorial ambitions in the South China Sea.

However, the US president's words on Syria had been the most eagerly anticipated, with Russia calling for international cooperation to defeat "Islamic State" ("IS"), and stating that Syrian President Bashar al-Assad must have a role. Obama appeared dismissive of any long term role for the Syrian leader, who he branded a "tyrant."

"There cannot be a return to the prewar status quo. Let's remember how this started. Assad reacted to peaceful protests by escalating repression and killing in turn created the environment for the current strife."

"When a dictator slaughters tens of thousands of his own people that is not one nation's internal affairs - it affects us all," said Obama, before turning his fire on IS.

"Likewise, when a terror group beheads captives, slaughter innocents and enslaves women… It is an assault on all our humanity."

Rare address from Russian leader

Putin's made his first speech before the General Assembly in a decade.

Putin effectively put the blame for IS at the door of the US, with many of the group being former members of the Iraqi military who were "thrown out into the street" after the 2003 US-led invasion of Iraq.

Others came from Libya, the statehood of which had been destroyed because of Western powers, while others had defected from the "so-called moderate" rebels, who had been supported by the West.

Putin was strongly critical of the US, saying it was a "grave mistake" not to cooperate with the Syrian government in the fight against IS. He urged the creation of a broad anti-terror coalition.

At a later meeting between the two leaders on the sidelines of the UN event, Obama is likely to want to focus also on the situation in Ukraine, where Kyiv, Washington and NATO accuse Moscow of backing and supplying a pro-Russian insurgency in the east of the country. The US has led efforts in imposing sanctions on Russia over its actions in Ukraine, which include the annexation of Crimea last year.

The Kremlin, which has always denied the accusations, however, said that the topic of Ukraine would be discussed only if time allowed, with the fight against Islamic State in Syria taking the foreground.

Driven by regional powers

Although the speeches by Obama and Putin are likely to draw the most attention, other world leaders among the some 160 expected to attend the meeting will also touch on globally sensitive topics.

UN Secretary General Ban Ki-moon said the Syrian conflict was "driven by regional powers and rivalries." He said five countries "hold the key" to a political solution to Syria: Russia, the U.S., Saudi Arabia, Turkey and Iran.

Ban said "innocent Syrians pay the price of more barrel bombs and terrorism" and there must be no impunity for "atrocious" crimes.

The UN leader also warned that resources to help those affected by humanitarian crises were in short supply. UN agencies had only half of what was needed to look after refugees in Iraq, South Sudan and Yemen, and only a half of the necessary finances to assist those in Syria.

DW