Mitt Romney accused President Barack Obama on Tuesday of trying to "paper over" deadly unrest and crises in the Middle East and failing to stand up to Iran in its quest for a nuclear bomb.

Shortly after the president laid out an unapologetic defense of his under-fire Arab Spring policy in a speech to the UN General Assembly in New York, the Republican nominee insisted the White House was shrinking from its responsibility to lead through strength in the volatile region.

He particularly took issue with Obama's weekend characterization of Middle East troubles as "bumps in the road" while countries like Egypt and Tunisia undergo sensitive transitions to democracy.

"Those developments include 20,000 people being killed in Syria, a Muslim Brotherhood president of Egypt, Iran on the cusp of becoming a nuclear power, and of course the assassination of our ambassador in Libya," Romney told CNN while campaigning in the critical battleground state of Ohio.

"I'm not sure whether any of those qualifies as a bump in the road. They certainly don't in my view."

"The White House's failure to acknowledge that the assassination of our ambassador was a terrorist attack, a terrorist event, suggests that they're trying to paper over the seriousness of what's happening in the Middle East."

His comment came despite the White House last week describing the assault on the US consulate in Benghazi, which killed four Americans including ambassador Chris Stevens, as a "terrorist attack" that could have links to Al-Qaeda.

Romney also said Obama has pledged time after time to prevent Iran and its President Mahmoud Ahmadinejad from acquiring a nuclear weapon, but that "it's very clear that his policies with regards to Iran have not dissuaded them from becoming nuclear by one iota."

The Republican also reiterated his charge that the Obama administration should be "indicting Ahmadinejad under the Genocide Convention for incitation to genocide, (and) treating the diplomats of Iran like the pariah they are, the way we treated the diplomats under South Africa under apartheid."