UN Secretary-General Ban Ki-moon has called on major powers to stop sending weapons to all sides in Syria, as he opened the annual UN General Assembly summit.
"I appeal to all states to stop fuelling the bloodshed and to end the arms flows to all parties," Ban told world leaders at the UNGA opening in New York on Tuesday.
The UN chief also called on Syrian President Bashar al-Assad and the opposition - and "all those in this hall with influence over them" - to work immediately to arrange a second Geneva conference aimed at reaching a political solution to the crisis that has wracked Syria for more than two years.
"Military victory is an illusion. The only answer is a political settlement," he said.
Ban said the response to last month's "heinous use of chemical weapons" outside Damascus "has created diplomatic momentum - the first signs of unity in far too long".
His appeal comes as the United States and Russia haggle over the language in a UN Security Council resolution meant to seal an agreement for Assad to give up chemical weapons.
US Secretary of State John Kerry was to meet his Russian counterpart Sergei Lavrov later in the day. Russia is the main supporter of Assad, while the rebels receive support from Western nations and Sunni Arab monarchies.
A top Russian diplomat said that the resolution would include the article of the UN Charter that allows the use of force or sanctions.
Among those due to address the assembly during Tuesday's session are the leaders of the United States, Turkey, France, Jordan, South Africa, Qatar, Iran, Lebanon and several other countries.