Iran’s foreign ministry spokesman said Monday Tehran is not satisfied with the pace of nuclear talks in Vienna but would not accept deadlines.

"Time is important to us, but it is not possible the other side moves like a turtle and we move at the speed of light," Saeed Khatibzadeh said.

He added that Iran wanted a “sustainable and reliable” agreement on reviving the 2015 nuclear deal with world powers, the JCPOA (Joint Comprehensive Plan of Action), with the talks encompassing “removal of sanctions, guarantees, verification, and nuclear issues.”

Khatibzadeh said Iran and the United States had exchanged views through informal written texts on all four issues. The US, which left the JCPOA in 2018 and imposed ‘maximum pressure’ sanctions on Iran, takes part indirectly in the Vienna process.

The spokesman emphasized that Iran would negotiate only with the JCPOA framework, and would not accept any intermediate steps towards reviving the 2015, nor enter into talks in Vienna over other matters. Khatibzadeh stressed the need to ensure Washington re-joined the JCPOA and did not again withdraw.

“We must all work to ensure that the United States’ return to the JCPOA is accompanied by necessary guarantees and verification,” he said. “The removal of sanctions should also be carried out effectively in accordance with the JCPOA. Such issues cannot materialize through an interim agreement.”

Bilateral and multilateral expert-level talks have been underway since the Vienna talks resumed on January 3 after a three-day break for New Year. The negotiation teams of Iran and Russia met Monday afternoon.

On Sunday, Iran's leader Ali Khamenei said that “holding talks and negotiating with the enemy at a certain juncture does not mean surrendering.” Khamenei ruled out direct talks with the US after President Donald Trump left the JCPOA in 2018, and Iran has insisted that talks on reviving the agreement take place within multilateral JCPOA structures.

There has been little news in the past week about the details of the negotiations. France and the United States have said there has been modest progress, although Iran and Russia have been insisting everything is on the right track.

The limited progress occurred after Western powers warned Iran that time is running out, and there are just “weeks not months” left to reach an agreement. Iran is enriching uranium while negotiations have continued for eight months. Growing stockpiles of fissile material can give Tehran more leverage in the talks.

The White house warned Tehran on Sunday against harming any US citizens, after top Iranian officials threatened revenge for the killing of Qasem Soleimani in a US drone strike in 2020.