European Union foreign policy chief Catherine Ashton says there is "no guarantee" that nuclear negotiations between Iran and the West will lead to a comprehensive deal when talks resume later this month.
Ashton spoke Sunday alongside Iranian Foreign Minister Mohammad Javad Zarif in the Iranian capital. She said meetings with Iranian officials will target bilateral ties, regional conflicts, human rights and the resumption of nuclear talks March 18.
Under an interim deal reached in November, Iran agreed to limit uranium enrichment for six months, in return for an easing of Western sanctions that have crippled the Iranian economy. The deal took effect January 20.
Western powers accuse Iran of efforts to develop nuclear weaponry with its ongoing research, while Tehran has repeatedly insisted its nuclear work has peaceful objectives.
On Sunday, Ashton called the upcoming talks on a comprehensive deal "difficult and challenging." Zarif said Iran is determined to reach an agreement, and says Tehran has shown "good will" in negotiations. He called on the West to reciprocate, and said a deal could be reached "in four or five months."
Under the interim deal, Iran agreed to cut back its production of enriched uranium, and to convert half of its stockpile of 20 percent enriched uranium to oxide.
The negotiations format involves Tehran and the so-called P5+1 -- Britain, France, the United States, Russia, China and Germany.