Iranian Supreme Leader Ayatollah Ali Khamenei has banned any further negotiations between Iran and the U.S., coming just months after Tehran signed a nuclear deal with the U.S and five other world powers.

"[Americans] have come up with a definition of negotiations with the Islamic Republic of Iran, [which] means infiltration and paving the way for imposition [of their demands on Iran]," Khamenei, the highest authority in Iran, said during a meeting with commanders and staff of the Islamic Revolution Guards Corps, according to his website. The U.S. is attempting to "change [our] officials' calculations and influence the thoughts of people, particularly youths, and everyone should be vigilant and conscious [to prevent this]."

"Negotiation with America is banned because such negotiation will not only have no advantage [for Iran], but will also entail numerous disadvantages" and would pave the way for the U.S. to infiltrate "into the country's economic, cultural, political and security domains," he added.

Khamenei's ban directly contradicts statements made by moderate Iranian President Hassan Rouhani, who said last month that the government was willing to hold talks with the U.S. on how to resolve the crisis in Syria, where Iran backs the Syrian government and the U.S. backs rebels fighting to overthrow it, reported Vice News.

Khamenei offered his support during the last 18 months of nuclear negotiations but has yet to publicly endorse the finalized agreement inked in July between Tehran and the U.S., Britain, China, Russia, France and Germany, according to Reuters.

The West has accused Iran of attempting to develop nuclear weapons, which Iran denies. The nuclear deal aims to curb Iran's nuclear program in exchange for the lifting of economic sanctions imposed by the U.S. and United Nations.

"In these negotiations, the opposite side sought to seize any opportunity for infiltration and take a step against the country's national interests. Of course, Iranian negotiators were fully aware, but Americans finally got the chance in some instances," Khamenei said.