WASHINGTON - The United States appears headed on a collision course with Iran that could lead to a war with "disastrous" consequences, a former adviser to ex-president Jimmy Carter warned.

"We think we are going to avoid war by moving toward compulsion," Zbignew Brzezinski, who was national security adviser to Carter in the late 1970s, told an audience at an Atlantic Council think tank event in Washington late on Tuesday.

"But the more you lean toward compulsion, the more the choice becomes war if it doesn't work. That narrows our options in a very dramatic way," said the former official, who remains an influential voice on US foreign policy.

Brzezinski said he was concerned about an escalation in "rhetoric", as the US approach to Iran's nuclear program appeared solely focused on forcing Teheran to comply with international demands, leaving Washington little flexibility.

"A lot of small decisions are being made which in the meantime narrow your freedom of choice in the future," he said.

Brzezinski warned repeatedly of his concerns that the US could stumble into a war with Iran.

"If we slide into a conflict with Iran, in this or that fashion, the consequences for us will be disastrous, disastrous on a massive scale and also globally at the same time," he said.

Brzezinski was in office in 1979 when US ally, the Shah of Iran, fell from power.

After the seizure of the US embassy in Iran and the taking of US hostages that same year, Brzezinski presided over a plan to rescue the captives but the military operation failed before it got off the ground.

Tensions have grown between Iran and the US in recent months as Washington has pushed for stricter sanctions to punish Teheran over its nuclear activities and amid speculation Israel may be weighing possible pre-emptive military action.

Tuesday's gathering featured four former national security advisers, including president Richard Nixon's powerful deputy Henry Kissinger.

The other former national security chiefs included Brent Scowcroft, who served under president George H.W. Bush, and Jim Jones, who until recently advised President Barack Obama.

Along with Brzezinski they all agreed that the world faced the most significant historical shift since the collapse of the Soviet Union two decades before, citing this year's wave of Arab uprisings.

The former senior White House advisers also voiced concerns that polarized US politics had undermined attempts to forge an effective foreign policy.

Brzezinski said there was a need "to galvanize this country into a deeper understanding" of international challenges facing the US.

"One of the most appalling things that I see is that we are more challenged than before in a more complex fashion," he said.

"Our public is driven by fear, ignorance, demagogy to a very high degree and that I think has a paralyzing effect in intelligent management," of foreign policy, he said.

Brzezinski, who endorsed Obama during the 2008 campaign, described what he called a "strange situation", with Obama and his fellow Democrats failing to assert leadership while their Republican rivals were advocating extreme or ill-informed policies.

"The party in power is frozen, and the party out of power is raving mad," he said.

Agence France-Presse