Iran's Oil Ministry denied a state media report that it had cut off oil exports to six EU states. "We deny this report ... If such a decision is made, it will be announced by Iran's Supreme National Security Council," a ministry spokesman said.

Iran's English language Press TV had said Tehran had halted oil deliveries to France, Portugal, Italy, Greece, Netherlands and Spain -- its biggest EU customers -- in retaliation for an EU ban on Iranian crude due to take effect in July.

The Republic is the world's No. 5 oil exporter, with 2.6 million barrels going abroad daily, about a fifth of it to EU countries.

Western sanctions are spreading to block Iran's oil exports and central bank financing of trade, and Tehran has resorted to barter to import staples like rice, cooking oil and tea, commodities traders say.

The Obama administration is putting pressure on the European Union and SWIFT, the global organisation that facilitates most of the world's cross-border payments, to expel Iranian banks from its network, a new step in the push to deprive Iran of funds, a US official said on Wednesday.

Expelling Iranian banks from the Belgium-based Society for Worldwide Interbank Financial Telecommunication would cut off one of Iran's few remaining avenues to do business abroad.

European banking regulators may meet SWIFT's board on Thursday to discuss the issue, two sources familiar with the matter said. SWIFT has said previously it is working to resolve the issue but is just a messaging system for its 10,000 users.

The most recent talks between world powers and Iran failed in January 2011 because of Tehran's unwillingness to discuss transparent limits on enrichment, as demanded by several UN Security Council resolutions passed since 2006.

The nuclear achievements proclaimed by Tehran involved a new line of uranium enrichment centrifuges and the loading of its first domestically produced batch of fuel into a research reactor that is expected to run out of imported stocks soon.

Tehran has for some years been developing and testing new generations of centrifuges to replace its outdated, erratic "P-1" model. In January it said it had successfully manufactured and tested its own fuel rods for use in nuclear power plants.