The United States is to unveil new sanctions against Iran Monday targeting its financial, oil and petro-chemical sectors, according to briefings by US officials to several American news outlets.

The reported sanctions aim to up the pressure on Tehran over its nuclear programme after a report by the UN atomic energy watchdog strongly suggesting Iran was researching nuclear weapons.

They also follow US allegations last month that Iranian officials were involved in a thwarted plot to kill the Saudi ambassador to Washington.

Iran has strongly denied both that it wants it a nuclear aresenal and that it had any hand in the alleged plot.

According to unidentified US officials quoted Monday on the websites of the Wall Street Journal and ABC television, the United States is to declare the Iranian financial sector of "primary money-laundering concern."

That phrase activates a section of the US Patriot Act, and would effectively warn European, Asian and Latin American businesses away from Iran if they want to continue to do business with the United States.

The Wall Street Journal noted that, when the same measure was used against Lebanese and North Korean banks in recent years, there were immediate runs on deposits in those countries.

ABC's website also said Britain and Canada would announce coordinated unilateral sanctions on Iran that would further tighten the financial noose.

The US officials giving the briefings further said that US sanctions would be applied to goods and services used in Iran's oil and petro-chemical industries, preventing foreign investment.

The New York Times last Friday quoted an unnamed Western official as saying European nations were expected to follow suit with their own sanctions later this week.

The reported move against Iran's financial sector generally appeared to be a way for Western nations to hobble Iran's economy without going directly after the obvious target: Iran's central bank.

US and European officials have said they were worried that hitting the central bank with sanctions could send oil prices abruptly soaring as Iran's big oil exports had a harder time getting to market.

Instead, the reported generalised sanction gave foreign businesses and governments time to phase out dealings with Iran's central bank, the US officials said in their briefings.

"This says: 'You should be thinking quite seriously about cutting off your ties to the central bank," one official was quoted as telling the Wall Street Journal.