Washington, Sep 23 (DPA) US President Barack Obama warned Wednesday that the US cannot solve the world's problems alone and urged other countries to take on a greater role.

Speaking at the opening of the UN General Assembly, Obama said countries must work together to tackle extremism, the proliferation of dangerous materials and global warming.

'This cannot be solely America's endeavour,' he said. 'Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone.'

Obama emphasized his administration's efforts to withdraw US forces from Iraq, reduce nuclear weapons stockpiles and to resolve the Israeli-Palestinian conflict.