The European Union, which presided over the Vienna talks, announced Monday's resumption.
Under President Donald Trump, the United States pulled out from the Vienna agreement in 2018. They reimposed severe sanctions on Iran. Iran has responded to the agreement by increasing purity and levels of uranium enrichment and stockpiles.
Joe Biden, the U.S. president, has indicated that he would like to join the agreement. Britain, France and Germany are still parties to the Iran accord and have been trying salvage it.
"Negotiations appear to be at the last stage which requires determination, energetic efforts by all participants to reach the destination point," Mikhail Ulyanov (Russia's delegate), stated on Twitter.
When talks stopped after one month, diplomats from three European countries stated that negotiations were at the end of their current stage and required political decisions.
Antony Blinken , the U.S. Secretary Of State, signed several waivers related to Iran's civilian nukes activities on Friday. This reverses Trump's decision not to repeal them.
The Iranian foreign minister welcomed the sanctions relief, but called it inadequate.