Tehran said in a letter to the UN that it was "determined to resolutely continue" enriching uranium. This came following an EU letter rebuking the government and a Russian firm suspending cooperation.
The government of Iran issued a letter to the United Nations on Thursday, announcing its intention to go ahead with its controversial ballistic missile program.
"Iran is determined to resolutely continue its activities related to ballistic missiles and space launch vehicles," Iranian UN envoy Majid Takhte Ravanchi wrote in a letter to Secretary-General Antonio Guterres.
Earlier, Iran's Foreign Minister Javad Zarif had scoffed at a letter from the UK, Germany, and France taking Tehran to task for not adhering to a 2015 landmark deal meant to curb Iranian nuclear ambitions. The letter called on Guterres to inform the Security Council in his next report that Iran's missile program is "inconsistent" with the implementation of the deal.
In a tweet, Zarif called it a "desperate falsehood to cover up their miserable incompetence in fulfilling the bare minimum of their own...obligations."
Tehran has criticized the EU for not fully implementing a barter mechanism the bloc said would shield Iran from some of the effects of reimposed US sanctions.
The war of words came at a particularly tense time between Iran and the West, after Iran suffered days of widespread protests against the regime that Tehran claims were promoted by Washington. The demonstrations, which began over a three-fold increase in fuel prices, became deadly when security services opened fire on protesters. Due to the lack of information and an internet blackout during the largest protests, it is difficult to know how many people were killed, though the US said on Thursday that it believes at least 1,000 people lost their lives. Thus far, Amnesty International has estimated a death toll of 208.
Russian firm suspends cooperation
Amidst the recent tensions, Iran appeared on Thursday to lose some of its backing from Russia, usually a key ally. Moscow's state-controlled nuclear fuel company, TVEL, has said it will suspend a joint research project with Iran because of its move to resume uranium enrichment.
TVEL said in a statement that Iran's decision to resume uranium enrichment at its Fordo facility makes it impossible to convert the facility to produce radioactive isotopes for medical purposes.