Iran’s Oil Ministry announced Sunday that it has stopped shipments to Britain and France, in retaliation for both countries’ support for boycotting  Iranian exports. The European Union imposed sanctions on Iran last month.

Iran’s Mehr news agency reported that the Oil Ministry had issued a warning to several other countries as well. EU nations were told to either order Iranian fuel now, or be cut off.

The EU buys approximately 18% of Iran’s oil exports. The sanctions imposed last month included an oil embargo which was to begin in July.

Iranian officials expressed defiance. “We have our own customers and have no problem to sell and export our crude oil to new customers,” Minister Ali Reza Nikzad-Rahbar said.

Iran has responded to growing international pressure with bluster. Last week Iranian President Mahmoud Ahmadinejad said his country would soon unveil “big new” nuclear developments, then revealed that 3,000 more centrifuges had been added to his country’s uranium enrichment effort. On Saturday Iran sent warships into the Mediterranean Sea for the second time in two years.