The US Senate on Thursday unanimously adopted harsh new economic sanctions on Iran, dismissing US officials' fears they risked fracturing global unity on blocking Tehran's suspected nuclear weapons program.

Lawmakers voted 100-0 to include the measure, which aims to cut off Iran's central bank from the global financial system, in a must-pass annual military spending bill poised for final approval.

Senators rebuffed an 11th-hour campaign from top aides to President Barack Obama who warned the legislation could shatter a growing but fragile global consensus on confronting the defiant Islamic republic over its nuclear drive.

The measure, crafted by Democratic Senator Robert Menendez and Republican Senator Mark Kirk, calls for freezing the US-based assets of financial institutions that do business with the central bank.

It would apply to non-US central banks that do so for the purpose of buying or selling petroleum -- Iran's chief source of revenues -- or related goods, amid growing fears that time is running short to solve the standoff peacefully.

"This is the right amendment, at the right time, sending the right message in the face of a very irresponsible regime," Kirk said.

"This is the maximum opportunity to have a peaceful diplomacy tool to stop Iran's march to nuclear weapons," said Menendez.

US officials have warned that depriving global markets of Iranian exports could send oil prices sharply higher, handing Tehran a windfall at a time when it has struggled to cope with painful international economic sanctions.

To address that, Kirk and Menendez's measure says the sanctions would only apply if Obama determines that there is sufficient oil from other producers to avoid disrupting global markets, and enables him to delay them if he determines that to be vital to US national security interests.

And Kirk said this week that Saudi Arabia's ambassador had told him of the kingdom's "great willingness" to boost its output to meet any resulting shortfall in supply.

The sanctions would not apply to sales of food, medicine and medical devices.

Earlier, Undersecretary of State for Political Affairs Wendy Sherman and Treasury Undersecretary for Terrorism and Financial Intelligence David Cohen warned the plan risked alienating key allies and inadvertently lining Iran's pockets.

"We all agree with the impulse, the sentiment, the objective, which is to really go at the jugular of Iran's economy," Sherman said in a frequently contentious hearing of the Senate Foreign Relations Committee.

"But there is absolutely a risk that, in fact, the price of oil would go up which would mean that Iran would, in fact, have more money to fuel its nuclear ambitions, not less," she said.

"Now, more than ever, it is imperative that we act in a way that does not threaten to fracture the international coalition of nations," Cohen said at a hearing just hours before lawmakers were to vote on the plan.

Sherman and Cohen's entreaties ran headlong into sharp criticisms from lawmakers impatient with the pace and scope of pressure on Iran and worried time was running short until the US nemesis joins the club of nuclear nations.

"You haven't shown us the robust effort, when the clock is ticking, to use that which we have given you," Menendez scolded, referring to past sanctions laws.

"We hear the words, we hear the talk, but we've wanted action for some time and it just hasn't happened," said Republican Senator James Risch, who warned of an "urgency gap" between the White House and Congress.

Senator Richard Lugar, the committee's top Republican, scoffed at concerns that the measure could alienate China, saying "they're not taking this very seriously anyway."

And, with the specter of military force as a last option lurking over the debate, Lugar declared "we're going to have to either contend with diplomacy with the Chinese or potential warfare with the Iranians."

Republican Senator Bob Corker asked whether Washington was "making plans with our friends towards military action" and sending "signals to Iran that, if these sanctions do not work, we really are prepared to use that option."

"Iran understands, and they read the newspapers and see what's happening. They understand it is a serious possibility," replied Sherman.

The Senate and House of Representatives were to hold negotiations to blend their rival versions of the underlying bill and send the compromise to Obama to sign into law.