Iran’s supreme leader decried “bullying governments” and bristled on Saturday at the idea of negotiating over the country’s nuclear program with the United States in an apparent response to a letter sent by President Trump earlier in the week.

Ayatollah Ali Khamenei, the leader, indirectly addressed Mr. Trump’s suggestion that Iran negotiate over its rapidly advancing nuclear program or face potential military action, while speaking at a meeting with government and military officials for Ramadan. Though he did not explicitly mention the letter, Mr. Trump or even the United States by name, it was clear he was speaking about Washington’s recent gesture.

“Some bullying governments insist on negotiations not to resolve issues but to impose,” Mr. Khamenei said, according to state media. He added that “negotiation is a path for them to make new demands, it’s not just nuclear issues to speak about the nuclear topic, they are making new demands which will definitely not be accepted by Iran.”

Speaking on Friday in the Oval Office, Mr. Trump suggested that Iran’s nuclear capabilities — which now include enough near-bomb-grade fuel to produce about six weapons — were reaching a critical point. He said he had offered the country a chance to negotiate or risk losing its program in a military strike.

The White House did not provide any specifics about the content of Mr. Trump’s letter, which the president said he sent on Wednesday.

Iranian officials are currently at odds over whether the country should negotiate over the program. While the ayatollah denounced Mr. Trump’s offer, other moderate and reformist leaders have spoken in favor of opening negotiations, including President Masoud Pezeshkian, who took office last year. Ultimately however, Mr. Khamenei, who has long said Iran cannot trust the United States, has the final say.

The 2015 nuclear accord negotiated by President Barack Obama had been effective, officials say. Iran had shipped nearly all its nuclear fuel stockpile out of the country, and international inspectors said the Iranians were abiding by the sharp restrictions on new production of nuclear fuel.

But Mr. Trump, who had repeatedly criticized the accord, withdrew from the nuclear agreement with Iran during his first term and reimposed heavy economic sanctions on the country, gambling that Tehran would respond by pleading for a new deal more advantageous to the United States.

Iran did not come back to the table, and now the program has reached a critical juncture, experts say.

Mr. Trump has also potentially undermined his proposal by upending two U.S. programs that for decades have worked to expose Iran’s atomic bomb programs. One program has since been restored, but experts worry the disruptions will hurt the worldwide struggle to contain nuclear proliferation.

Farnaz Fassihi contributed reporting.