United Nations, Sep 22 - Warning that the global economic recession could hinder the ability of countries to take necessary steps to combat climate change, President Barack Obama Tuesday told world leaders 'we are determined to act'.

'The journey is hard. And we don't have much time left to make it,' Obama said in brief remarks at a climate summit convened by US Secretary-General Ban Ki-moon.

The US has put climate at the top of the diplomatic agenda with countries across regions, from China and India to Brazil and Mexico, he said.

Speaking after Ban admonished leaders to put aside differences and move more quickly, Obama sought to show US resolve ahead of crucial talks in Copenhagen in December, when nations will try to reach a new global treaty to address climate change.

'We understand the gravity of the climate threat. We are determined to act,' he said. 'And we will meet our responsibility to future generations.'

'We seek sweeping but necessary change in the midst of a global recession, where every nation's most immediate priority is reviving their economy and putting their people back to work,' Obama said.

He said nations are concerned about reviving their economies amid a global recession, but added that difficulty is no excuse for inaction.