U.S. President Barack Obama is imposing tough new sanctions against Iran and its central bank in a move designed to freeze the country's assets amid growing nuclear tensions.

Obama has signed an executive order that will cut the Islamic republic off from finance and commerce under U.S. jurisdiction, reasoning that "deceptive practices of the Central Bank of Iran and other Iranian banks" warranted the strict measures.

The president's letter to Congress accused Iran of trying to "conceal transactions of sanctioned parties" and said that poor anti-money laundering enforcement there posed an "unacceptable risk" to the global financial system.

The U.S. Treasury Department said in a release that under the order, Iran's assests within the jurisdiction of U.S. persons or entities will be frozen.

The executive order is designed to enforce central bank sanctions in a defence bill passed last year and signed into law by Obama. The purpose of the bill was to restrict funding for Tehran's nuclear program and its alleged financing of international terrorism.

Diplomatic solution sought

In an interview with NBC, Obama confirmed the U.S. has a projected timeline for how long it might take Iran to reach nuclear weapons capability. But he said there's still much uncertainty about the political reality in what is considered to be one of world's most diplomatically isolated countries.

"Do we know all of the dynamics inside of Iran? Absolutely not," he said in the interview, which aired Monday. "Iran itself is a lot more divided now than it was. Knowing who is making decisions at any given time inside of Iran is tough."

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Growing anxiety from the international community over Iran's nuclear ambitions has prompted the U.S. to further tighten sanctions against the country. (Associated Press/Mehr News Agency/Majid Asgaripour)

The newly announced sanctions come against a tense backdrop in which the U.S. has continued to call on Iran to scrap its nuclear program because of international concern the country is intent to make weapons.

For its part, Iran has continually insisted its nuclear pursuits are strictly peaceful.

Recent speculation about a possible Israeli strike planned against Iran's nuclear sites has added to the pressure, but Obama said Sunday he doesn't believe Israel has made up its mind about an attack, and he's still hoping for a diplomatic resolution.

Military intervention not ruled out

Even so, he said, every option for dealing with Iran was still on the table, which would include the possibility of military intervention.

"We are prepared to exercise these options should they arise," Obama said.

The sanctions amendment in the defence bill compelled U.S. punishment of foreign financial institutions that conduct transactions through Iran's central bank in order to import petroleum. Several U.S. allies in Europe and Asia engage in such business with Iran.

Under the law, Obama still has the option of waiving any penalties for national security reasons.

In recent weeks, both the U.S. and European Union have imposed harsher sanctions on Iran's oil sector, the lifeblood of its economy.

With files from The Associated Press