Iran’s supreme leader has accused the US of being “a liar” and “backstabber”, and effectively ruled out any future negotiations with the American government under his leadership.

Ayatollah Seyed Ali Khamenei, who proclaimed “death to America” in March last year, told a crowd of school pupils and teachers in Tehran that talks with Washington were now inconceivable.

"Negotiations with the US will not resolve our problems, because firstly, it is a liar, disloyal, a cheater and a backstabber,” he said.

“And secondly, the US itself is crisis-stricken – and how can a crisis-hit country resolve another country's problems?

“The policy and essence of the arrogant US government is based on over-ambitiousness and for years it has applied the policy in different parts of the world, particularly in the western Asia region and pre-revolution Iran.

“Now the Americans are in a situation that they have become desperate about the developments in Syria, Iraq, Lebanon, Yemen and North Africa. Isn't this situation a crisis?"

Ayatollah Khamenei also said the recent US presidential debates between Donald Trump and Hillary Clinton revealed "the collapse of humanitarian values" in America and showed his estimations were correct about the state of US politics.

"Their comments showed they are sufficient for the annihilation of the reputation of the United States," he said, according to CNN. "The US system is far away from values of humanity."

According to reports, Iran recently publicly streamed the US presidential debates as "anti-American propaganda".

Iran is marking the anniversary of the 1979 siege of the US embassy in Tehran, during which a group of Iranian students held 52 American diplomats and citizens hostage for over 14 months amid a backlash against US influence in Iran.

Relations between Iran and the US have been notoriously difficult since the 1979 revolution, but appeared to improve following a “historic” deal struck by president Barack Obama in April last year, during which Iran agreed to reduce its nuclear capabilities in exchange for a loosening of economic sanctions.

New York protests against Iran nuclear deal Show all 10 1 /10 New York protests against Iran nuclear deal New York protests against Iran nuclear deal New York A woman holds a poster as she takes part in a rally on Times Square in New York opposing the nuclear deal with Iran New York protests against Iran nuclear deal New York An inflatable mushroom cloud stands among demonstrators during a rally apposing the nuclear deal with Iran New York protests against Iran nuclear deal New York Protesters rally against the nuclear deal with Iran in Times Square New York protests against Iran nuclear deal New York A member of the Neturei Karta Orthodox Jews sect is escorted away by New York City Police during a rally near Times Square to demand that Congress vote down the proposed US deal with Iran in New York New York protests against Iran nuclear deal New York A woman shouts slogans during a rally against the nuclear deal with Iran in Times Square in New York New York protests against Iran nuclear deal New York A protestor holds a placard during a demonstration and rally apposing the nuclear deal with Iran in Times Square New York protests against Iran nuclear deal New York Some of several thousand protestors crowd into 7th Avenue at 42nd street as they demonstrate during a rally apposing the nuclear deal with Iran New York protests against Iran nuclear deal New York A woman holds a placard as she joins several thousand other protestors to demonstrate during a rally apposing the nuclear deal with Iran New York protests against Iran nuclear deal New York Protesters rallied against the Iran nuclear deal in New York's Times Square KENA BETANCUR/AFP/Getty Images New York protests against Iran nuclear deal New York Protestors shout slogans as they demonstrate during a rally apposing the nuclear deal with Iran

Before the agreement was struck, Ayatollah Khamenei told a crowd of supporters: “Of course yes, death to America, because America is the original source of pressure.The politics of America is to create insecurity. They insist on putting pressure on our dear people’s economy.”