Iran's Supreme Leader Ayatollah Ali Khamenei has endorsed a landmark nuclear deal reached with world powers, but warned against "ambiguities" in the agreement.
Khamenei, who has the final say on all major Iranian policies, backed the deal in a letter to President Hassan Rouhani that was read on state TV on Wednesday.
Until now he had publicly declined to approve or reject the deal while expressing support for Iran's negotiators.
Iran's highest authority said the United States and European Union should clearly announce the elimination of sanctions against Iran, and warned that the deal had several structural weak points.
He said he approved the decision of the country's top security committee, the Supreme National Security Council, to implement the nuclear agreement, but that it must be "tightly controlled" and monitored "to prevent significant damage" to country's future.
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He also warned his country's government to be vigilant, saying the United States cannot be trusted.
The agreement reached in July with the US, Britain, France, China, Russia and Germany would curb Iran's nuclear activities in exchange for the lifting of crippling international sanctions.
Western nations have long suspected Iran of pursuing nuclear weapons alongside its civilian programme, charges rejected by Tehran, which insists its programme is entirely peaceful.