The UN Security Council's inability to pass a resolution on Syria has encouraged the government to step up its assault on the opposition and launch an "indiscriminate attack" on civilians in the city of Homs, the UN human rights chief has said.

Navi Pillay, the UN High Commissioner for Human Rights, said President Bashar al-Assad's violent crackdown on dissidents indicated crimes against humanity had taken place since March 2011 and were continuing.

Al Jazeera's Cath Turner reports from New York