AFP - Britain will seek a global ban on investment in Iran's oil, gas and financial sectors unless Tehran agrees to abandon its uranium enrichment activities, Prime Minister Gordon Brown said Monday.

LONDON (AFP) — Britain will seek a global ban on investment in Iran's oil, gas and financial sectors unless Tehran agrees to abandon its uranium enrichment activities, Prime Minister Gordon Brown said Monday.

Brown described the Islamic republic as "the greatest immediate threat to non-proliferation" and again said it had a choice between complying with the international community or being ostracised.

"We will lead in seeking tougher sanctions both at the UN and in the European Union, including on oil and gas investment and the financial sector," he said in a speech at the Lord Mayor of London's annual banquet.

"Iran should be in no doubt about the seriousness of our purpose."

Brown said further sanctions were conditional on the conclusion of two reports by Europe's foreign policy chief Javier Solana and the UN atomic watchdog, both of which are due out later this month.

In addition, Brown threw his weight behind calls for a nuclear fuel "bank" to aid non-nuclear states in gaining access to new sources of energy, provided they renounce nuclear weapons and meeting international treaties.

Although he has threatened to push for tougher measures against Iran if it does not stop enriching uranium, Brown has until now not given more specific details.

In a television interview Sunday, he again asserted that he was ruling nothing out in the stand-off, amid speculation about a possible strategic military strike against Iran's nuclear facilities.

The comments also come as Britain, France, Germany, the United States, Russia and China prepare to back a third UN Security Council resolution against Iran.

Overall, the set-piece speech -- in which Britain's prime minister normally addresses key foreign policy issues -- saw Brown call for what he called "hard-headed internationalism" on the world stage.

Such a steadfast multi-lateral approach was vital to help tackle global threats from extremism and climate change to poverty and unrest in places like Myanmar, Pakistan and Darfur, he added.

But to do so, reform of international bodies such as the United Nations, International Monetary Fund and World Bank, was vital -- a popular theme of his predecessor Tony Blair.

On Britain's relationship with the United States and Europe, he also picked up Blair's argument that London's close ties with Washington should not be a bar to partnership with Brussels.

And after describing himself as a "life-long admirer of America", he welcomed a thaw in frosty relations between France and Germany with the United States that set in during the run-up to the Iraq war in 2003.

"In the years ahead ... I believe that Europe and America have the best chance for many decades to achieve together historic progress," he added.