Iran’s Supreme Leader Ayatollah Ali Khamenei gestures as he delivers a speech during a gathering by Iranian forces, in Tehran, on Wednesday.

Iran’s Supreme Leader Ayatollah Ali Khamenei on Wednesday banned any further negotiations between Iran and the United States, putting the breaks on moderates hoping to end Iran’s isolation after reaching a nuclear deal with world powers in July.

Khamenei, the highest authority in the Islamic Republic, already said last month there would be no more talks with the United States after the nuclear deal, but has not previously declared an outright ban.

His statements directly contradict those of moderate Iranian President Hassan Rouhani, who says his government is ready to hold talks with the United States on how to resolve the conflict in Syria, where the two countries back opposing sides.

“Negotiations with the United States open gates to their economic, cultural, political and security influence. Even during the nuclear negotiations they tried to harm our national interests.,” Khamenei was quoted as saying on his website.

“Our negotiators were vigilant but the Americans took advantage of a few chances,” he said.

Khamenei has not publicly endorsed the nuclear agreement with the US, Germany, France, Britain, China and Russia that settled a standoff of more than a decade.

In his address to Revolutionary Guards Navy commanders, Khamenei said talks with the US brought only disadvantages to Iran.

“Through negotiations Americans seek to influence Iran … but there are naive people in Iran who don’t understand this,” Khamenei was quoted as saying to the IRGC commanders, who are also running Iran’s military involvement in Syria.

“We are in a critical situation now as the enemies are trying to change the mentality of our officials and our people on the revolution and our national interests,” Khamenei told the Guards.