Representatives from major world powers and Iran continued talks on the 2015 Joint Comprehensive Plan of Action (JCPOA) on Friday in Vienna, with the U.S. and Germany both expressing cautious optimism about the state of the ongoing negotiations.

"The United States team put forward a very serious idea and demonstrated a seriousness of purpose on coming back into compliance if Iran comes back into compliance," a top U.S. State Department official in the talks told reporters Friday. 

The official said the U.S. is now waiting for Iran to reciprocate its efforts.

What are European officials saying about the talks?

German Foreign Minister Heiko Maas described the ongoing talks as "constructive."

"All sides showed a willingness to work with the necessary sincerity towards the same goal — the full implementation of the nuclear deal with Iran," Maas told German outlet RND in comments published on Saturday. "It won't be easy. We are only at the beginning of intensive negotiations." 

EU diplomat Enrique Mora called the talks "constructive and results-oriented."  Permanent Representative of Russia to International Organizations in Vienna Mikhail Ulyanov said JCPOA participants "noted with satisfaction the initial progress made."

Iran says U.S. must lift all Trump-era sanctions 

A tweet from Iranian Foreign Minister Javad Zarif earlier in the day urged Washington to return to "full compliance first." He said "anti-JCPOA" sanctions implemented under former President Donald Trump must be removed.

Iranian Deputy Foreign Minister Abbas Araghchi said prior to Friday's negotiations there "are signs that the U.S. is about to revise its position and lift sanctions."

Although the United States was an original signatory to the deal in 2015, Trump ordered the country's withdrawal from the agreement in 2018. The U.S. maintained a "maximum pressure" policy towards Iran during the Trump era, severing its connection to the global financial system.

President Joe Biden has previously said his administration would be unwilling to remove sanctions unless Iran ceases its uranium enrichment.

Negotiations in Vienna are slated to resume on Wednesday.