Iran’s supreme leader said President Donald Trump is a “clown” who only pretends to support the Iranian people, as he addressed Friday prayers in Tehran for the first time since 2012.

Ayatollah Ali Khamenei said Mr Trump will “push a poisonous dagger” into the nation’s back.

He said the outpouring of grief at the funeral for Iran’s top general, who was killed in a US airstrike earlier this month, shows that Iranians support the Islamic Republic.

He said Iran’s retaliatory missile attack on US troops in Iraq earlier this month was a “blow to America’s image” as a superpower.

The cleric said America had “cowardly” killed the most effective commander in the fight against the Islamic State group when it targeted General Qassem Soleimani in a US airstrike in Baghdad.

In response, Iran launched a barrage of ballistic missiles targeting US troops in Iraq, without causing serious injuries.

As Iran’s Revolutionary Guard braced for an American counterattack that never came, it mistakenly shot down a Ukrainian jetliner shortly after it took off from Tehran’s international airport, killing all 176 passengers on board, mostly Iranians.

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Ayatollah Ali Khamenei wept at the funeral of Qassem Soleimani (Iran Press/AP)

Ayatollah Ali Khamenei has held the country’s top office since 1989 and has the final say on all major decisions.

The 80-year-old leader openly wept at the funeral of Gen Soleimani and vowed “harsh retaliation” against the United States.

Authorities concealed their role in the tragedy for three days, initially blaming the crash on a technical problem.

Their admission of responsibility triggered days of street protests, which security forces dispersed with live ammunition and tear gas.

Tensions between Iran and the United States have steadily escalated since President Donald Trump withdrew the US from Iran’s 2015 nuclear deal with world powers, which had imposed restrictions on its nuclear programme in exchange for the lifting of international sanctions.

The White House has since imposed crippling sanctions on Iran, including its vital oil and gas industry, pushing the country into an economic crisis that has ignited several waves of sporadic, leaderless protests.

Mr Trump has openly encouraged the protesters, even tweeting in Farsi, hoping that the protests and the sanctions will bring about fundamental change in a long-time adversary.

After Mr Soleimani was killed in a US airstrike in Baghdad, Iran announced it would no longer be bound by the limitations in the nuclear agreement.

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Mr Khamenei met tje family of Iranian Revolutionary Guard General Qassem Soleimani following the latter’s death in a US air strike (AP)

European countries who have been trying to salvage the deal responded earlier this week by invoking a dispute mechanism that is aimed at bringing Iran back into compliance and could result in even more sanctions.

Mr Khamenei was always sceptical of the nuclear agreement, arguing that the United States could not be trusted.

But he allowed President Hassan Rouhani, a relative moderate, to conclude the agreement with then US president Barack Obama.

Since Mr Trump’s withdrawal, he has said there can be no negotiations with the United States.

President Donald Trump authorised the air strike that killed Qassem Soleimani (Evan Vucci/AP)

Mr Khamenei last delivered a Friday sermon in February 2012, when he called Israel a “cancerous tumour” and vowed to support anyone confronting it.

He also warned against any US strikes on Iran over its nuclear programme, saying the US would be damaged “10 times over”.