Iran has stopped oil sales to France and the UK as tensions continue to rise over its nuclear programme.
State media said the oil ministry had "cut" all exports to the two countries.
The ministry spokesperson said the country would "sell our oil to new customers".
The move follows an agreement by the European Union to stop importing Iranian oil after 1 July.
The deal was agreed last month, but its introduction was delayed to allow member states to find alternative suppliers.
It had been announced on Wednesday that Iran had stopped exporting oil to France, Greece, the Netherlands, Portugal, Spain and Italy, but that was later denied by the oil ministry.
Around 18% of Iran's oil exports currently go to the EU. Less than 1% of its oil exports go to the UK, and around 2% go to France.
Iran has the fourth largest oil reserves in the world. It's 137bn barrels of proven oil reserves are more than Iraq, the United Arab Emirates and Kuwait.
On Wednesday Iran announced a "breakthrough" in its nuclear research, and broadcast live footage of its scientists loading domestically made nuclear fuel roads into a research reactor for the first time, at a ceremony attended by President Mahmoud Ahmadinejad.
"We began enriching uranium to 20% in order to make fuel rods because Western countries are not ready to help us," said deputy head of Iran's Supreme National Security Counci Ali Baqeri, according to a student news agency and Reuters.
Iran says it has made the 20% enriched uranium because it wanted to produce isotopes to treat cancer.
The research reactor is believed to be used for medical purposes and agricultural products. It previously ran on Argentinian fuel rods but it did not reach deal to extend the trade deal.
But in a report last year the International Atomic Energy Agency, which reports to the United Nations, said that Iran was fixated on producing a nuclear bomb and was closer than ever to succeeding.
Iran has refused to suspend its nuclear research, heightening tensions in the region.
British foreign secretary William Hague said on Sunday it would be a mistake for Israel to launch a military strike against Iran in an attempt to destroy its alleged nuclear weapons programme.
Speaking on the BBC's Andrew Marr programme, Hague said Israel should put its efforts into making sure there were effective sanctions against Tehran.
"I don't think the wise thing for Israel to do is launch a military attack," he said.
Hague said that Israel had not shown the British government any plans for an attack on Iran but acknowledged there had been some discussion by Israeli politicians in public about the possibility of a strike.
"They are not sharing any plans with us, they are not asking us to join in any plans, we are not calling for any military action against Iran," he said.
He added: "Our approach is 100% diplomatic and economics focused."
On Saturday Hague warned that Iran's nuclear ambitions could plunge the world into "a new Cold War" with the Middle East.Suggest a correction