Tehran said Sunday it will keep talking with world powers on its disputed nuclear programme despite a US move to blacklist Iranian companies for evading sanctions.
"We are pursuing the negotiations seriously and of course we will give a well-considered, purposeful, smart and proper reaction to any inappropriate and unconstructive move," Foreign Minister Mohammad Javad Zarif wrote on his Facebook page.
This was despite the Americans having made "inappropriate moves to which we gave the appropriate response by considering all aspects of the issue".
"The negotiations and achieving a result are a difficult task and will definitely have a lot of ups and downs. We have predicted that from the very beginning."
He later told CBS television in the United States: "The process has been derailed, the process has not died."
Zaris also told the network's Face the Nation programme that Iran is committed to the Geneva accord, adding however: "It takes two to tango."
The United States blacklisted a dozen overseas companies and individuals on Thursday for evading its sanctions imposed on Iran to halt what the West sees as its bid to build a nuclear bomb.
Senior US officials argued the move was taken under an existing sanctions regime which had forced Tehran to negotiations that led to an interim deal under which it agreed last month to freeze parts of its nuclear programme.
The measures, which angered Iran and prompted its negotiating team to withdraw from the talks in Vienna, have drawn strong criticism in the Islamic republic.
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Since Saturday, conservative newspapers have condemned the "violation of the Geneva deal" by the American administration.
Some hardline students from the Islamist militia (Basij) have written an open letter to Zarif urging him to "defend the dignity" of Iran "by giving a firm response."
In the letter, published Sunday by Iranian newspapers, they also backed the decision of the negotiating team to quit the Vienna talks.
Zarif vowed to answer at the right time domestic critics who were using his "necessary silence" to voice their displeasure at the nuclear deal reached with the six world powers in Geneva on November 24.
"Some friends who were not happy with the Geneva joint action programme have already announced its premature death, which is more the expression of their desire rather than the truth," he said on Facebook.
"The negotiating team has a more important responsibility... and is ready to remain silent against unjust and unfair accusations for the sake of national interests, but will answer to all the criticism and ambiguity at the right time."
Sadegh Zibakalam, a reformist political analyst, said anti-American slogans were part of the political strategy of the conservatives.
"If we pull the rug of anti-Americanism from under the feet of the conservatives, they would have nothing left to say," Ilna news agency quoted him as saying.
Under the interim deal reached in Geneva, Iran agreed to freeze parts of its suspect nuclear programme in return for some relief from Western sanctions as it negotiates a comprehensive accord to allay suspicions that it seeks a weapons capability.
The United States also agreed to refrain from slapping new sanctions on Iran.