Mitt Romney said the attack on the US consulate in Libya is an issue in the presidential campaign because Americans wonder why it took the Obama administration so long to acknowledge it was a terrorist act.

America, caught by surprise by the ferocious September 11 attack against the US consulate in Libya that killed the US ambassador and three other countrymen, is bracing itself for more potential violence in parts of the Muslim world today.

Protesters angered by an anti-Islam film have stormed the US Embassy compound in Yemen’s capital, two days after America’s ambassador was gunned down at the US Consulate in Libya.

The US government is investigating whether the attack on the US Consulate in Libya in which America’s ambassador was gunned down was a planned terrorist strike to mark the anniversary of the September 11 2001 attacks rather than a spontaneous mob enraged over an anti-Islam YouTube video.

US President Barack Obama has condemned the attack on the Benghazi consulate and a safe house refuge in which the US ambassador to Libya and three embassy staff were killed.