Syria unrest: World leaders urge President Assad to go

US President Obama has openly called for the resignation of Syria's Bashar al-Assad, after weeks of condemning the Syrian leader's crackdown on protesters.

The leaders of the UK, France, Germany and the EU joined Mr Obama in demanding President Assad step down from power.

Meanwhile, UN investigators have said the use of violence in Syria "may amount to crimes against humanity".

James Robbins reports.