Iran has proclaimed advances in nuclear know-how, including new centrifuges able to enrich uranium much faster, a move that may hasten a drift towards confrontation with the West over suspicions it is seeking the means to make atomic bombs.

Tehran was driving home its resolve to pursue a nuclear programme its hardline Islamic clerical leaders see as a pillar of power, protection and prestige despite Western sanctions that are inflicting increasing damage on its oil-based economy.

Iran also aimed to show that increased sanctions have failed to stop it making progress in nuclear technology.

However, Iran's Arabic-language Al Alam television said the government had handed a letter to EU foreign policy chief Catherine Ashton expressing readiness to "hold new talks over its nuclear programme in a constructive way".

Ms Ashton's spokeswoman has confirmed receipt of the letter, saying she was evaluating it and would consult with the United States, Russia, China and other partners among the big powers.

Iranian officials have long refused to negotiate curbs on its programme, saying it aims solely to produce electricity for booming domestic demand in OPEC's number two oil-exporting state.

The most recent talks between world powers and Iran collapsed in January 2011 when they could not agree an agenda.

The US and Israel have not ruled out military action against Iran if diplomacy and sanctions are ultimately judged futile in reining in its nuclear activity.

Iran rejects oil export ban to EU

Underlining the high stakes and at times nervous confusion arising from the nuclear stand-off, Iran's oil ministry denied a media report that it had cut off oil exports to six EU states.

Iran's English language Press TV 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.