President Barack Obama has vowed to bring to justice those who carried out the attack that killed the US ambassador to Libya.

But he said the US consulate attack in Benghazi would not harm ties between the US and the new Libyan government.

It has sparked a political row in the US, with rival Mitt Romney criticising Mr Obama before the president hit back.

Ambassador J Christopher Stevens died after gunmen stormed the consulate amid protests over an anti-Islamic film.

Meanwhile, protesters in Egypt have clashed with security forces after crowds returned to the US embassy in Cairo for a second evening of demonstrations over the film.

Riot police fired tear gas at protesters, some of whom were seen carrying petrol bombs, witnesses said.