A framework nuclear deal reached with world powers last week is no guarantee a full agreement will be reached by the end of June, Iran's supreme leader Ayatollah Ali Khamenei said Thursday.
"What has been done so far does not guarantee an agreement, nor its contents, nor even that the negotiations will continue to the end," Khamenei, who has the final word on all matters of state, said according to his official website.
Last week, Tehran and the six powers agreed on the framework of a deal to be finalised by the end of June reining in Iran's nuclear programme in return for the lifting of international sanctions.
"Everything is in the detail, it may be that the other side, which is unfair, wants to limit our country in the details," Khamenei said.
He said he had not taken any position until now as "there is nothing to take a stance on".
"Officials say that nothing has been done yet and there is nothing binding. I am neither for nor against."
Under the outline text agreed last week between Iran and the six powers -- the United States, Britain, China, France and Russia plus Germany -- Iran must significantly reduce its number of centrifuges in exchange for a suspension of sanctions.
The outline was a major breakthrough in a 12-year international crisis over Iran's nuclear programme, although a final deal has yet to be reached.
Khamenei said: "I have always supported and still support the Iranian negotiating team.
"I welcome any agreement that protects the interests and greatness of the nation, but having no agreement is more honourable than an agreement in which the interests and greatness of the nation is damaged."
He said that retaining a civil nuclear industry in any agreement with the powers was vital for Iran's future development.
"The nuclear industry is a necessity, for energy production, for desalination, and in the fields of medicine, agriculture and other sectors," he said.