ANKARA (Reuters) – Supreme Leader Ayatollah Ali Khamenei on Wednesday approved the Iranian government’s nuclear deal with world powers but said Tehran should not give up core elements of its atomic program until allegations of past military dimensions had been settled.

In a letter to President Hassan Rouhani, whose pragmatist approach opened the door to nuclear diplomacy with the West, Khamenei ordered the July 14 agreement to be implemented, subject to certain security conditions the Iranian parliament stipulated in a law passed last week.

Under the Vienna agreement, Iran is to curb sensitive parts of its nuclear program to help ensure it cannot be diverted into developing bombs, in exchange for a removal of sanctions that have isolated the Islamic Republic and hobbled its economy.

Khamenei’s green light was the last procedural hurdle to carrying out a deal that ended a decade-long stand-off which raised fears of a wider Middle East war.

But the Supreme Leader has ruled out any detente with the West beyond the nuclear deal, and he said Iran would stop implementing it if the six powers – the United States, Britain, France, Germany China and Russia – imposed any new sanctions.

“Any comments suggesting the sanctions structure will remain in place or (new) sanctions will be imposed, at any level and under any pretext, would be (considered by Iran) a violation of the deal,” Khamenei said in the letter published on his website.

He said implementation of the deal should be “tightly controlled and monitored” because of some “ambiguities” in it.

“Lack of tight control could bring significant damage for the present and the future of the country,” he said, while praising the efforts of Rouhani’s negotiating team.

POSSIBLE MILITARY ASPECTS

The United States and the European Union took formal legal steps on Sunday that will rescind sanctions once Iran meets certain conditions such as reducing the number of centrifuges used to enrich uranium, and its enriched-uranium stockpile.

Another condition will be a resolution of a U.N. nuclear watchdog inquiry into whether Iran conducted atom bomb research at a military complex in the past – “possible military dimensions (PMD)” to the program, as the agency terms it.

On that point, Khamenei said that until U.N. inspectors settled the PMD issue, Iran should delay sending its stockpile of enriched uranium abroad and reconfiguring a heavy water reactor to ensure it cannot make bomb-grade plutonium.

The International Atomic Energy Agency finished collecting samples from Iran’s Parchin military complex earlier this month and is expected to announce its conclusions on PMD by Dec. 15.

Iran has long denied covertly researching bombs and says its nuclear program has always been for civilian energy purposes.

“Any action regarding Arak (reactor) and dispatching uranium abroad … will take place after the PMD (possible military dimensions) file is closed,” Khamenei said in the letter.

Iran agreed with the powers to fill the Arak reactor’s core with concrete so that it could not yield plutonium, which along with highly enriched uranium constitutes the standard fuel for nuclear bombs.

Iran is also required to export more than 90 percent of its refined uranium stocks, keeping just 300 kg of the material enriched to 3.67 percent fissile purity – suitable for running civilian nuclear power plants – for 15 years.

Since the deal was struck, Khamenei, who holds together Iran’s multi-tiered, faction-ridden power structure, has ruled out normalizing relations with the United States, overriding Rouhani’s expressed wish to pursue further areas of cooperation.

In comments meant to reassure hardline acolytes particularly in the security services, Khamenei said U.S. President Barack Obama had sent him two letters pledging America had no intention of toppling the Islamic Republic’s clerical establishment.

“But this was soon proved a lie … Neither on the nuclear issue nor in any other cases has America taken any position except hostility and trouble (towards Iran). Therefore any change in the future is unlikely,” Khamenei’s statement read.

(Writing by Parisa Hafezi and Sam Wilkin; Editing by William Maclean and Mark Heinrich)