U.S. President Barack Obama's policy on Iran represents his single worst foreign policy failure, Republican presidential candidate Mitt Romney said in an interview on Sunday, saying that Iran was closer to having "nuclear capability" than when Obama took office in 2008.

Romney's comments, made during an interview to NBC's "Meet the Press," came after, on Friday, U.S. Senators John McCain, Joe Lieberman and Lindsay Graham called for a far tougher position against Iran over its suspected, and seemingly inexorable, drive toward acquiring nuclear weapons capability.

McCain argued that with the notable exception of the case of Apartheid South Africa, "sanctions, when we look at history, rarely work," and in the case of Iran that's exacerbated by a sense that the nuclear program has the people's support.

"We have applied very tough economic sanctions on Iran and they have clearly affected the economy of Iran, but they have not affected the nuclear program one iota," marveled Lieberman.

"By its recalcitrance Iran is presenting the rest of the world with only two choices: Do we accept a nuclear Iran and try to contain it … or do we take military action? That's a fateful decision that's got to be made in the months ahead," he added.

Speaking to "Meet the Press" on Sunday, Romney spoke of Obama's foreign policy, saying that "perhaps [Obama's] biggest failure is as it relates to the greatest threat that America faces and the world faces, which is a nuclear Iran."

"The president has not drawn us further away from a nuclear Iran. In fact, Iran is closer to having a weapon, closer to having nuclear capability than when he took office, "Romney said, reiterating that this represented Obama's "greatest failure."

Romney's comments came after U.S. House of Representatives Intelligence Committee Chairman Mike Rogers confirmed that during a meeting held in Jerusalem two weeks ago, Prime Minister Benjamin Netanyahu harshly criticized U.S. Ambassador to Israel Dan Shapiro over Obama's policy concerning Iran.

Netanyahu's spokesman Liran Dan said in response: "As we said last week, the report is incorrect and we have nothing more to add."

The incident was reported last week in the Israeli daily Yedioth Ahronoth. The report said Shapiro responded to Netanyahu's attacks politely, but decisively. Interviewing to Israel's channel 2 news a few days later, Shapiro denied any confrontation took place.