Iran's chief nuclear negotiator, Saeed Jalili, warned the EU in a letter on Thursday that new sanctions will have "repercussions" on talks over his country's atomic activities.
The letter, made public by Iranian state media, "warned the West of repercussions of taking action which is far removed from the logic in the talks and of using illegal methods against the Iranian nation."
It was sent on the day the United States ratcheted up sanctions on foreign companies doing business with Iran's central bank, and just ahead of the full implementation on Sunday of an EU-wide embargo on Iran's oil exports which has been phased in since it was announced on January 23.
Iran and world powers this year revived negotiations over Tehran's disputed nuclear programme, but have reached an impasse after three rounds of talks.
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The next meeting has been downgraded to the level of experts and is scheduled to take place in Istanbul on Tuesday.
Jalili's letter was addressed to EU foreign policy chief Catherine Ashton, who represents the so-called P5+1 group (the United States, Britain, France, Russia and China, plus Germany) engaging Iran.
In it, he said Iran stands ready to "share initiatives that can make the talks a success and move them forward," according to the Farsi version of the letter.
But he added that such progress depended on "cooperation and a framework of building trust."
Jalili wrote that "if the constructive talks are damaged, the responsibility will be with the party that is implementing illegal tools instead of logic in the negotiations."
Iran considers four sets of sanctions imposed by the UN Security Council, and a raft of additional sanctions imposed by the United States and the European Union, to be "illegal" and it has insisted it will resist them.