World leaders pledge another 30,000 United Nations peacekeeping troops

World leaders glided though the opening of a UN gathering Monday that aims to wrestle with crises like a historic flood of refugees, the rise of groups like the Islamic State and the headache that binds them Syria's conflict.

The UN secretary general called for the Syrian crisis to be referred to the International Criminal Court, while Iranian President Hassan Rouhani said its recent nuclear deal with world powers had a broader goal, of suggesting "a new and constructive way to recreate the international order."

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Chinese President Xi Jinping made a $1-billion pledge for UN peace efforts and a promise to contribute 8,000 troops for a peacekeeping standby force, a move that could make China one of the largest players in UN peacekeeping efforts.

Xi's pledge comes as China is trying to show it is a responsible international player amid concern over its growing military might and territorial disputes in the Asia-Pacific region.

More than 50 countries have pledged to contribute more than 30,000 new troops and police to UN peacekeeping, which significantly exceeds the goal of 10,000 personnel the U.S. initially set, U.S. President Barack Obama said.

Rise of the Islamic State

Jordan's King Abdullah II, meanwhile, made a heartfelt defence of the kinder side of the Muslim world in the face of "the outlaws of Islam that operate globally today."

The king has called the rise of extremist groups like the Islamic State, and the crises [that] have caused, "a third world war, and I believe we must respond with equal intensity."

Jordan borders both Syria and Iraq, and Syrian refugees now make up 20 per cent of Jordan's population. Iraq and Turkey also groan under the strain of millions of refugees.

The assembly's Secretary GeneralBan Ki-moon's insisted on a political solution to the conflict in Syria, now well into its fifth year with more than a quarter of a million people killed.

5 countries 'hold the key'

Ban said five countries "hold the key" to the political solution: Russia, the U.S., Saudi Arabia, Turkey and Iran.

U.S. President Barack Obama said of Syrian leader Bashar Assad, "when a dictator slaughters tens of thousands of his own people, that is not a matter of a nation's internal affairs."

The U.S. is prepared to work with any country, including Russia and Iran, to resolve Syria's conflict, its president said, although relations between Obama and Russian President Vladimir Putin have been strained.

The global humanitarian system is not broken; it is broke.- UN Secretary General Ban Ki-moon

Putin called for the creation of a broad international coalition against terror, following his country's surprising moves in recent weeks to increase its military presence in Syria and to share intelligence on the Islamic State group with Iran, Iraq and Syria.

The Russian leader dismissed the West's concerns about his country's ambitions in Syria, "as if they have no ambitions at all," and he called it "an enormous mistake to refuse to co-operate" with the Syrian government.

Iran's Rouhani, who entered the chamber smiling, appeared to align with Putin's call for a UN Security Council resolution consolidating the fight against terror, while France plans to discuss a proposal by Turkey and members of the Syrian opposition for a no-fly zone in northern Syria.

France "will look at what the demarcation would be, how this zone could be secured and what our partners think," French President Francois Hollande said on Monday.

Other crises at the centre of this week's discussions include the related refugee and migrant crisis, the largest since the upheaval of the Second World War.

But Ban warned that resources to address these crises are dangerously low. "The global humanitarian system is not broken; it is broke," he said.

The UN has just half of what it needs to help people in Iraq, South Sudan and Yemen, and just a third of what's needed for Syria.

Barrel bombs

Assad's tactics of dropping deadly barrel bombs on opposition-held neighbourhoods of Syria are the main driver behind the refugee crisis, speakers heard at a panel at UN headquarters.

The executive director of Human Rights Watch, urged the international community to put an end toAssad's indiscriminate use of the bombs, saying the bombing also undermines the war against the Islamic State group.

"It is a recruitment bonanza for ISIS because the group can claim to be standing up to these atrocities," Kenneth Roth, said, using an acronym for the group. He said the explosives are being used for the sole purpose of terrorizing the population and have played a major role in fuelling the exodus of migrants.

Barrel bombs are makeshift shrapnel-packed explosive devices that Syrian forces continue use and are responsible for the deaths of thousands of civilians over the past four years.

"We are tired of collecting limbs," said Raed Saleh, head of the Syrian Civil Defense. "We ask ourselves as we dig out people from the rubble, whether we are next."

Castro calls for sanctions to end

Cuban President Raul Castro, meanwhile, used his first address to the United Nations to highlight that normal relations with the U.S. would only be possible if Washington ended its trade embargo on his country, returned the military base at Guantanamo and ended anti-communist broadcasts beamed into the island.

With diplomatic ties now restored, a healthy relationship "will only be achieved with the end of the economic, commercial and financial blockade," Castro said in his first ever address to the United Nations.