President Obama 'not optimistic' about Syria's immediate future

Obama also warned that the city of Aleppo would likely fall soon

US President Barack Obama has said he was "not optimistic" about Syria's immediate future as the regime and its Russian backers launch a sustained bombardment of civilians in Aleppo.

"I am not optimistic about the short term prospects in Syria," Obama said at a press conference in Peru on Sunday, warning Syria's second city was likely to fall.

"Once Russia and Iran made a decision to back (Bashar al) Assad in a brutal air campaign... It was very hard to see a way in which even a trained and committed moderate opposition could hold its ground for long periods of time," said Obama.