TEHRAN — Iran’s highest leader lashed out at the United States on Monday, saying talk that American influences would pour into the country on a wave of positive feelings over the nuclear deal is nothing more than a “hollow fantasy.”

The supreme leader, Ayatollah Ali Khamenei, speaking to a group at his downtown Tehran office complex, warned that Iran would remain as vigilant as ever in guarding against the “economic, political and cultural influence” of the United States, according to his website, Khamenei.ir. “We will block all attempts of penetration of Iran,” he said.

That message is at odds with the one emanating from many other officials, led by President Hassan Rouhani, who are saying it is time for new relations with the United States. Supporters of the government have been arguing that the revolution’s trademark slogan of “Death to America,” still shouted during Friday prayers and at state-backed demonstrations, has become obsolete.

Hard-liners have mostly been silent on the nuclear agreement, but in editorials they have warned that the United States is planning to export its cultural mores and business practices to Iran. “We thought that they would bring Boeing technology, but they want to bring McDonald’s,” Gen. Mohammad Reza Naghdi, a leader of the Islamic Revolutionary Guards Corps, said last week. McDonald’s is not currently allowed to operate in Iran.