TEHRAN (AFP) - European Union foreign policy chief Catherine Ashton said on Sunday there is "no guarantee" that talks with Iran on its disputed nuclear programme will lead to a comprehensive agreement.

"This interim agreement is really important but not as important as a comprehensive agreement (which is)... difficult, challenging, and there is no guarantee that we will succeed," Ms Ashton told a joint news conference in Tehran with Iranian Foreign Minister Mohammad Javad Zarif.