Iran has said progress was made after talks in Tehran with senior inspectors from the UN International Atomic Energy Agency (IAEA).
"Intensive negotiations were held ... There was good progress made," IRNA news agency quoted Ali Asghar Soltanieh, Iran’s ambassador to the IAEA, as saying on Thursday.
"The two sides agreed to hold the next round of talks on January 16 in Tehran," Soltanieh added.
There was no immediate comment from the inspectors after Thursday’s meeting over Iran's disputed nuclear programme, and no sign its inspectors would gain access to the Parchin military complex as requested.
Western governments accuse Iran of seeking to develop atomic weapons through its nuclear programme and have strengthened sanctions against it.
Iran insists its programme is for peaceful purposes only.
The IAEA believes Iran has conducted explosives tests with possible nuclear applications at Parchin facility near Tehran and has repeatedly asked for access.
The talks were the first between the UN agency and Iran since August and the outcome could give some indication whether Iran is willing to address the concerns over its nuclear work.
US toughens sanctions
Earlier on Thursday, the Obama administration announced it had stiffened penalties on Iran over its nuclear programme by blacklisting 12 companies and individuals for their work in transferring sensitive technology and uranium enrichment.
The departments of State and Treasury imposed the sanctions against seven more companies and five more people, freezing any assets they may have in US jurisdictions and barring Americans from doing business with them.
The Treasury Department says they were targeted because they provide the Iranian government with "unique goods, technology and services" related to the nuclear programme that violates UN Security Council resolutions.
"So long as Iran continues to pursue a nuclear programme in defiance of multiple UN Security Council resolutions, the US will target those involved in Iran's illicit enrichment activities,'' the Treasury Department said in a statement.