Iranians form a human chain around a uranium facility to show their support for Iran's nuclear program [Reuters]

The United States, Britain and Canada will impose new financial sanctions on Iran in an effort to pressure Tehran to halt its suspected nuclear weapons program.

A US official on Monday said the financial and energy sanctions will target Iranian companies, the Revolutionary Guard force and Iran's petrochemicals sector. The official spoke on condition of anonymity, because of the sensitivity of the issue.

The sanctions will likely be officially announced later on Monday by Hillary Clinton, the US Secretary of State, according to the official, .

Britain ordered all financial institutions in the United Kingdom to stop doing business with Iranian counterparts, as well as with the central bank of Iran, Britain's finance ministry said.

The financial sanctions will not target oil trading, a source familiar with the terms of the sanctions said on Monday.

"They definitely won't target oil trading. That's a step too far ... The world needs Iranian exports and there are too many interests tied up," the source said.

The source said that the sanctions were in response to the International Atomic Energy Agency's (IAEA) latest report on Iran, which highlighted fresh concerns about the possible military dimensions of Iran's nuclear programme.

George Osborne, the UK finance minister, said: "This follows the International Atomic Energy Agency's report uncovering evidence of Iran's development of nuclear weapons technology. It is also a response to calls from the Financial Action Task Force for countries to strengthen safeguards to protect their financial sectors from money laundering and financing of terrorism risks emanating from Iran."

He continued: "We believe that the Iranian regime's actions pose a significant threat to the UK's national security and the international community. Today's announcement is a further step to preventing the Iranian regime from acquiring nuclear weapons."