LIMA - US President Barack Obama said on Sunday that chaos in Syria could persist for 'quite some time' and that Russian and Iranian support for President Bashar al-Assad's air campaign had emboldened the Syrian leader's crackdown on rebels. 'I am not optimistic about the short-term prospects in Syria,' Obama said at a news conference in Lima at the conclusion of a summit with leaders of Pacific Rim countries. 'Once Russia and Iran made a decision to back Assad and a brutal air campaign and essentially a pacification of Aleppo regardless of civilian casualties, children being killed or wounded, schools or hospitals being destroyed, then 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,' he said.