"The US is threatening militarism. In my opinion, this threat is unwise," Khamenei said in a meeting with students. "Iran is capable of retaliating and will definitely inflict a blow."

The remarks came as local media in Iran reported that foreign minister Abbas Araghchi had received Trump's letter, which was delivered by senior United Arab Emirates official Anwar Gargash.

Khamenei, who noted he had not yet personally received the letter, said its invitation to talks was aimed at "deceiving the world's public opinion" by presenting the United States as ready to negotiate and Iran as unwilling.

"We sat down and negotiated for several years, this same person threw the finished, completed and signed agreement off the table and tore it up," he added, referring to Washington's withdrawal from a landmark 2015 nuclear deal during Trump's first term in office, which ended in 2021.

Since returning to the White House in January, Trump has called for a new nuclear deal with Tehran while reinstating his "maximum pressure" sanctions policy over concerns Iran is seeking to develop nuclear weapons.

Tehran denies the allegations.

Iran has officially ruled out direct talks as long as sanctions remain, and on Wednesday Khamenei said talks with the US "will not lift sanctions... and will make the sanctions knot tighter".

"Regarding nuclear weapons, it is said that we will not let Iran obtain nuclear weapons. If we wanted to make nuclear weapons, America could not stop us," Khamenei said.

"The fact that we do not have nuclear weapons and are not seeking nuclear weapons is because we ourselves do not want them."

Khamenei, who has final say in state matters, said Iran "was not seeking war, but if someone takes action, our response will be decisive and certain".