US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met for bilateral talks Friday on the sidelines of the World Economic Forum in Davos.

US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met for bilateral talks Friday on the sidelines of the World Economic Forum in Davos.

"Secretary Kerry and Iranian foreign minister Zarif just concluded an hour-long meeting in Davos," a State Department source said, without providing more details.

The top-level meeting occurred as Iranian and US diplomats officially resumed talks in Switzerland on intensifying efforts to reach a deal on the future of Tehran's nuclear program.

Two days of meetings between Iran's deputy foreign minister Abbas Araghchi and top US negotiator Wendy Sherman began Friday morning in Zurich.

EU political director Helga Schmid was also taking part in the meetings, he added.

 The talks are taking place less than a week after Araghchi met with Sherman and representatives for five other global powers in Geneva in a bid to hammer out a comprehensive deal which would rein in Tehran's nuclear programme in exchange for relief from a tight network of sanctions.

Kerry and Zarif already met last week in Geneva and then again in Paris to discuss the nuclear negotiations.

Iran and the P5+1 (China, Russia, France, Britain and the US – plus Germany) have been holding talks to secure a final comprehensive deal over Iranian nuclear work.

Since an interim deal was agreed in Geneva in November 2013, the negotiating sides have missed two self-imposed deadlines to ink a final agreement.

Iran and the P5+1 countries now seek to reach a high-level political agreement by March 1 and to confirm the full technical details of the accord by July 1.