United Nations Secretary-General Ban Ki-moon stressed the need for global cooperation to tackle the world's most pressing issues including the crisis in Syria and elsewhere, beyond conflict, accelerating achievement of the Millennium Development Goals (MDGs). He was speaking to reporters ahead of the 68th United Nations General Assembly (UNGA) session.

"This is a crucial period for global cooperation. Syria is the biggest peace, security and humanitarian challenge we face. Let us be clear: the use of chemical weapons in Syria is only the tip of the iceberg," Ban told the press in New York.

It is sad that the international community has been unable to help the Syrian people to enjoy their genuine freedom and peace during the last two-and-a-half years, Ban said.

Evidence gathered by U.N. investigators regarding the use of chemical weapons in Syria on Aug 21 are "indisputable and overwhelming."

"Therefore, we must not take the "business as usual" [approach]. I sincerely hope that Russia and the United States demonstrate their leadership at this time, particularly the countries of the permanent members of the Security Council," he said.

He went on to say that he hoped the Council took action quickly because, "while we welcome the belated accession by the Syrian Government to the Chemical Weapons Convention, there are many obligations [which] must be implemented."

"Next week, as world leaders gather here, I will make a strong appeal to Member States for action now," Ban said.

Next week's General Assembly annual debate will be attended by some 130 Heads of State as well as foreign ministers.

The Secretary-General said he will use the occasion to call on world leaders to "uphold their political and moral responsibilities to serve, to listen, to invest, to respond to the rising and justifiable demands of people across the world for lives of freedom and prosperity."

"We have a full agenda. But the events of the past days have shown once again the power of the United Nations to uncover the facts - to resolve differences - to help avoid bloodshed and forge consensus for peace and progress," he said.

"We must harness that spirit for action to address our immediate crises and achieve our longer-term goals," the Secretary-General said.

Issues that will require urgent attention include climate change, boosting efforts to accelerate the achievement of the MDGs and the shaping of the post-2015 development agenda.

He pointed out that, "The situation in Afghanistan, Egypt, Mali and the Central African Republic will also be high on the agenda of UNGA.

"... as we assess new approaches we are taking in peacekeeping, diplomacy and support for countries in transition."

The Middle East diplomatic Quartet - comprised of the UN, the European Union, Russia and the United States - will be meeting for the first time in more than a year to support the resumption of Israeli-Palestinian negotiations.

On the development front, the UNGA will hold a high-level session on disabilities and development this year. The Secretary-General stressed the importance of taking into account the needs and aspirations of people with disabilities - who make up 15 per cent of the global population.

"The next week or two will bring many opportunities for common progress. But success will depend on ever deeper levels of cooperation - and contributions from our partners," Ban said.