Fed by diplomatic tensions and election-year politics, talk about a coming conflict with Iran has reached a fever pitch in the US capital.

Speculation of a possible war with Iran ebbs and flows, but a confluence of events has served to fuel dire predictions among politicians and pundits that war may be on the horizon -- either by necessity or by accident.

Some of the same hawkish voices that portrayed Saddam Hussein's regime in Iraq as a dire threat requiring urgent military action are now warning that the United States must be prepared for war with Iran, while accusing President Barack Obama of lacking backbone.

John Yoo, a former Justice Department official under ex-president George W. Bush, has called on Republican presidential candidates to "begin preparing the case for a military strike to destroy Iran's nuclear program."

Calling it an "unavoidable challenge," Yoo wrote last week in the National Review that the United States would have legal grounds to strike at Iran's nuclear sites -- similar to the arguments made before the invasion of Iraq.

"It can argue that destroying Iran's nuclear weapons is a combination of self-defense and protecting international security," said Yoo, who during Bush's tenure backed broad presidential powers to wage war and deny rights to terror suspects.

Republican presidential hopeful Mitt Romney has made a clear commitment to use military force if necessary, promising that if he wins the White House, Iran will not have nuclear weapons.

Both in the United States and Israel, lawmakers and commentators warn that time is running out on the Iranian "nuclear clock" and that at some point over the next year, economic sanctions will have to be abandoned in favor of bombing raids to stop Iran from securing the bomb.

Senator Lindsey Graham and other Republicans have said any US military action would have to be broader than a few "surgical" strikes on nuclear facilities.

"Their capability is so redundant you'd have to do more than go after the nuclear program, you have to neuter this regime, destroy the air force, sink their navy, go after the Revolution Guard and try to get people in the country to overthrow the regime. We need a regime change," Graham told the CBS show "Face the Nation" in November.

"If they get a nuclear weapon the world is going to go into darkness," he said.

Despite rising tensions with Tehran and tough rhetoric from lawmakers, US military and defense chiefs have warned repeatedly that air strikes on Iran would, at best, only delay Tehran's nuclear efforts by a few years while carrying huge risks.

Analysts who oppose military action worry the United States could stumble into a war with Iran because a strategy focused on pressure and punitive sanctions may leave no diplomatic way out of the crisis.

"We are in such an escalatory cycle, if we just continue on this path much longer, we will essentially sleepwalk into a war," Trita Parsi, author of a book on US policy toward Iran, told AFP.

In "A Single Roll of the Dice: Obamas Diplomacy with Iran," Parsi argues the Obama administration tried a diplomatic approach but gave up too soon, partly because the Iranian regime's crackdown on street protests in 2009 made it politically impossible for the White House to pursue an opening with Tehran.

"It made a bad atmosphere much, much worse," said Parsi, president of the National Iranian American Council.

Obama faces similar political pressures that plagued former president Bill Clinton over Iraq in the 1990s, when Republicans blasted sanctions on Saddam Hussein as ineffective, according to Parsi.

Some US officials privately worry about sliding into an unintended war, as does Zbigniew Brzezinski, the former national security advisor during Jimmy Carter's presidency in the 1970s.

"We think we are going to avoid war by moving towards compulsion," Brzezinski said last month.

"But the more you lean towards compulsion, the more the choice becomes war if it doesnt work. That narrows our options in a very dramatic way."

Shortly before retiring, the former top-ranking US officer, Admiral Mike Mullen, worried a lack of communication between the two countries' militaries could turn an incident into a potential conflict.

"We are not talking to Iran. So we dont understand each other," Mullen said in September. "If something happens, its virtually assured that we wont get it right, that there will be miscalculations."