Republican presidential candidate Mitt Romney said that, after consulting with Israeli Prime Minister Benjamin Netanyahu on Friday, he does not believe military action will be required to prevent Iran from developing nuclear weapons.

Romney called Iran’s nuclear development “the greatest national security threat that we face,” but he stopped short of endorsing Netanyahu’s comments this week that a military strike might be necessary to keep Iran from obtaining nuclear capability.

However, Romney told reporters aboard his campaign plane Friday that it was difficult to determine during his telephone call with Netanyahu whether there was a difference between their so-called “red lines” on ordering military action.

“I do not believe that in the final analysis we will have to use military action. I certainly hope we don’t have to. I can’t take that option off the table. It must be something which is known by the Iranians as a possible tool to be employed to prevent them from becoming nuclear. But I certainly hope that we can prevent any military action from having to be taken,” Romney told reporters aboard an afternoon flight from Philadelphia to Bedford, a suburb of Boston.

When a reporter asked how Romney’s position on Iran’s nuclear arms development differs from President Obama’s, Romney accused the president of having “moved over time.”

“From the very beginning, I thought crippling sanctions needed to be put in place,” Romney said. Of Obama, he added, “his words more recently are more consistent with the words I’ve been speaking for some time, and we’ll see what actions he pursues.”

Obama and Netanyahu also spoke Friday by telephone. The White House issued a statement saying the conversation “underscored that they are in full agreement on the shared goal of preventing Iran from obtaining a nuclear weapon.”

Romney said he would have taken action to indict Iranian leader Mahmoud Ahmadinejad under the Geneva Conventions for “incitation of genocide.” And he added that he would also take action against Iran’s diplomats to “treat them like the pariah I think they are, the same way we treated South African diplomats under apartheid.”

Romney and Netanyahu spoke by phone as the nominee drove from his midday campaign rally in Wayne, Pa., to Philadelphia International Airport. Their friendship dates to the 1970s, when the two were colleagues at the Boston Consulting Group, and Romney told reporters that he they “renewed our personal acquaintances again,” talking about their families and Romney’s visit to Israel in July.

Romney said he complimented Netanyahu on his speech to the United Nations, but joked that he considered ribbing the prime minister over the quality of the poster he showed at the U.N. to illustrate his “red line” on Iran.

“I suggested that his graphic was not up to the normal Boston Consulting Group standards,” Romney said. Laughing, he corrected himself. “No, I didn’t actually do that. But I was thinking that.”