Iran's nuclear deal with world powers is holding a year after it was agreed but more needs to be done to ensure its full implementation, a top Iranian negotiator said Wednesday.

"The total process has been relatively satisfactory despite the difficulties that we see in the implementation," Hamid Baeidinejad told a press conference in Tehran for the first anniversary of the agreement.

"We belive that the deal has not been violated so far and efforts continue to resolve the remaining issues," Baeidinejad said.

The deal between Iran and the P5+1 group of powers (Britain, China, France, Germany, Russia and the United States) limited Tehran's atomic programme in return for the lifting of some international sanctions, which took effect in January.

There has been some disappointment in Iran that the lifting of the sanctions has not yet led to significant investments, with many international investors and banks still wary of doing business with the Islamic republic.

Despite the lifting of nuclear-related penalties, Washington and the European Union maintain some sanctions on Iran over its human rights record and ballistic missile testing.

Asked if Iran had oversold the deal to its people, Baeidinejad said: "We knew exactly what was agreed upon in the deal and what was not."

He said Tehran "had more expectations on the removal of economic, banking and financial restrictions, but despite all these deficiencies there is a feeling of hope inside our country to remove these obstacles" through more talks.

"We will not agree to anything less than the full implementation of the JCPOA," he said, referring to the Joint Comprehensive Plan of Action, the official name of the agreement.

The agreement caused "great optimism" in Iran on "unrelated issues", Baeidinejad said, but those expectations are "fortunately being balanced and adjusted to reality".

President Hassan Rouhani on Wednesday also praised the "new atmosphere" created by the accord, saying it can lead to "better economic, defence, and technological activity" for Iran.

"In some fields, including banking, we still haven't reached the expected level, although good steps have been taken in this regard and some connections have been made with big international banks," Rouhani was quoted as saying by official news agency IRNA.