Iran's Supreme Leader Ayatollah Ali Khamenei has endorsed the country's nuclear deal with world powers but warned the agreement suffers from ambiguities and "structural weaknesses."
In a letter to Iranian President Hassan Rouhani that was read on state television, Khamenei said such weaknesses could damage the country in the present and the future.
He urged Iranian officials to be vigilant in guarding against inconsistencies in the agreement.
The agreement has been the subject of fierce debate in Iran, with hardliners arguing Iranian negotiators gave too much ground in discussions with the United States, Britain, France, Russia, China and Germany.
Negotiators finalized the deal in July. Once fully implemented, it will lift all nuclear-related international sanctions against Iran in return for strict curbs on its atomic program.
On Sunday, U.S. President Barack Obama ordered the government to start preparing to lift sanctions against Iran.
Obama also said Iran has started carrying out its side of the deal, removing centrifuges, slashing its uranium stockpiles, and filling the Arak heavy water nuclear reactor with concrete, all to ensure it cannot build a nuclear weapon.
The United States and its Western allies have long suspected Iran's atomic program is aimed at building a nuclear weapon. Iran insists the program is only for peaceful purposes such as energy production and medical research.