Iran's Supreme Leader Ayatollah Ali Khamenei declared on Wednesday that Tehran will never give up its nuclear program, the BBC reported.
Speaking to a gathering of nuclear scientists, Khamenei said Iran had agreed to talks with the West to "break the hostile atmosphere" with the international community and to show that it was not seeking nuclear weapons.
"These talks need to continue but all must know that despite continuation of the talks, activities of the Islamic Republic of Iran in the field of nuclear research and development won't be halted at all," said Khamenei, according to the BBC.
Telling negotiators not to "accept any coercive words from the other party," he added, "None of the country's nuclear achievements can be stopped, and no one has the right to bargain over it."
Under a six-month interim deal which was reached between Iran and six world powers in November, the Islamic Republic agreed to freeze its uranium enrichment program in return for sanctions relief, including the transfer of some $4.2 billion in frozen overseas funds.
That interim agreement is meant to lead to a final accord that minimizes any potential Iranian nuclear weapons threat in return for a full lifting of sanctions.
The sides met again for another round of talks in Vienna on Wednesday, following which Iranian Foreign Minister Javad Zarif said the two sides were up to 60% in agreement.
A senior U.S. official was less upbeat but said all sides were committed to keep trying.
Throughout the negotiating process, Iran has insisted that it has a right to enrich uranium and has remained adamant that it will not give up that right.
Khamenei has said in the past that Iran has no intention of developing nuclear weapons but if it wanted to, the United States could not thwart it.
Decisions about Iran's disputed nuclear drive rest with Khamenei, who has issued a fatwa (Islamic religious ruling) declaring that possession of atomic weapons is a "sin" banned by religion.