"The Secretary General has just announced that the Joint Special Representative for Syria, Lakhdar Brahimi, is on his way to Russia to help him push, on margins of the G20 summit in Saint Petersburg, for the International Conference on Syria," the UN spokesperson said in a statement.

The United Nations is making a desperate new bid for a Syria peace conference even as the United States prepares a possible military strike, according to diplomats.

"It is time for the parties to stop fighting and start talking. The Syrian people need peace," Ban said in a lecture at Saint Petersburg State University Wednesday.

US President Obama will hold meetings on the sidelines of the G20 with French President Francois Hollande, the main foreign backer of a strike on Syria, as well as the leaders of China and Japan.

While no formal bilateral sit-down meeting is planned with Russia’s Putin, a White House official suggested there would likely be some kind of more informal conversation.

Russian and US ties have sunk to a new low since the Cold War, over deep seated divisions over Syria, Russia's granting of asylum to US fugitive intelligence leaker Edward Snowden and a string of Russian laws seen as repressive.

International aid agency Oxfam also called on the G20 to overcome their differences on Syria saying: "The timing of this G20 is critical. Leaders in St Petersburg must not let ordinary Syrians down."

NJF/NJF