Iran's supreme leader has accused the US of plotting to overthrow Tehran`s clerical leadership in a frosty response to an overture by President Barack Obama for better cultural ties with the country.

Ayatollah Ali Khamenei did not reject outright Mr Obama's offer, saying Iran would keep an eye on Washington's intentions.

But the supreme leader said that so far, Washington's offers of engagement with Tehran have been a "deception".

The exchange was a sign of how Mr Obama's hopes for dialogue with Iran have broken down amid Tehran's rejection of Western demands over its nuclear programme and its heavy crackdown on the opposition following disputed presidential elections last June.

In a message to coincide with the Iranian new year Nowruz, Mr Obama told the Iranian people that Americans want better cultural exchanges with Iran - but he also criticised Tehran`s leadership for "turning its back" on US overtures.

Khamenei, who has the final say on all political matters in Iran, lashed back in a nationally televised address on Sunday, telling the US: "You cannot speak about peace and friendship while plotting to hit Iran."

In particular, he denounced US criticism of the post-election crackdown. Iran has arrested thousands in the wake of widespread protests that erupted against Iranian President Mahmoud Ahmadinejad's victory in the vote, which the opposition claims was fraudulent.

Referring to Mr Obama's message, Khamenei said, "We will examine the issue with sharp vision to determine if it really is a friendship hand and a friendly intention or hostile one in a deceptive framework."