"The Americans should know threats will get them nowhere when confronting Iran," Ayatollah Ali Khamenei said in his live annual televised speech marking Nowruz, the Persian New Year.

He said Americans "and others should know that if they do anything malign to the Iranian nation, they will get a hard slap".

On March 7, Trump said he had written to Khamenei, urging negotiations with Tehran over its nuclear programme and warning of potential military action if it refuses.

On Thursday, Foreign Minister Abbas Araghchi said the letter was "more of a threat", but also said it appeared to offer opportunities.

Araghchi added that Tehran is weighing its response which will be issued in the coming days.

On Wednesday, US news website Axios, citing a US official and other sources, reported that Trump's letter set a "two-month deadline for reaching a new nuclear deal".

It did not specify a start or end date of the two-month period.

Khamenei has previously dismissed Trump's overtures for talks, accusing the US president of attempting to deceive global public opinion by portraying the United States as willing to negotiate and Iran as unwilling to engage.

Trump, who began his second term in January, has reinstated his policy of "maximum pressure" against Tehran.

During his first term, he unilaterally withdrew the United States in 2018 from the landmark nuclear deal between Iran and world powers and reimposed sweeping economic sanctions on Tehran.

Iran initially adhered to the deal for a year after Trump's withdrawal but then started scaling back its own commitments, increasing uranium enrichment levels up to 60 percent.

The current level far exceeds the 3.67 percent limit set under the deal, and is much closer to the 90 percent threshold required for weapons-grade material.

Efforts to revive the nuclear deal have so far failed.

Tehran accuses Trump of contradictory approaches, and has repeatedly ruled out direct talks with Washington under pressure.

Iran "definitely will not negotiate directly while facing pressure, threats, and increased sanctions," Araghchi said on Thursday.