
The Foreign Office has hit out at Iran for a 'flagrant violation of international law' after the UK ambassador to the country was arrested during a protest in the capital Tehran.

Diplomat Rob Macaire was present during demonstrations against Ayatollah Khamenei in front of Tehran’s Amir Kabir University and was arrested after allegedly 'organising, provoking and directing radical actions', according to local reports.

Thousands had gathered to demand the supreme leader's resignation after his regime admitted it had mistakenly shot down a civilian passenger plane during retaliation against the US' assassination of Qasem Soleimani.

Mr Macaire, a diplomat with 30 years experience, was released following more than an hour in detention.

In a strongly worded statement, Foreign Secretary Dominic Raab warned Iran that it needed to make a choice between becoming a 'pariah' state or to 'deescalate tensions' with the west.

'The arrest of our Ambassador in Tehran without grounds or explanation is a flagrant violation of international law. The Iranian government is at a cross-roads moment,' said Mr Raab.

The UK ambassador to Iran Rob Macaire was arrested earlier this evening during violent protests in Tehran in response to Ayatollah Seyed Ali Khamenei's regime admitting it had mistakenly shot down a civilian passenger plane

Following a more than an hour in detention, Mr Macaire was then released. MailOnline have contacted the Foreign Office for comment but they were unable to provide a comment

Iranians protest against the government after a vigil held for the victims of Flight 752 turned into an anti-government protest outside Amirkabir University in Tehran, Iran

'It can continue its march towards pariah status with all the political and economic isolation that entails, or take steps to deescalate tensions and engage in a diplomatic path forwards.'

Mr Macaire was appointed to the Ambassador role in April 2018, replacing Nicholas Hopton.

Angry crowds gathered in at least four locations across Tehran tonight, chanting 'death to liars' and calling for the country's supreme leader to step down over the tragic military blunder, video from the scene shows.

What began as mournful vigils for Iranian lives lost on the flight soon turned to outrage and protest against the regime, and riot police quickly cracked down, firing tear gas into the crowd.

'Death to the Islamic Republic' protesters chanted, as the regime's security forces allegedly used ambulances to sneak heavily armed paramilitary police into the middle of crowds to disperse the demonstration.

Ukrainian Airlines Flight 752 was carrying 176 people, at least 130 of them Iranian citizens, when it was shot down by hapless Iranian Revolutionary Guard air defense forces shortly after taking off from Tehran on January 8.

President Donald Trump tonight tweeted his support for the Iranian protestors, writing in Farsi that his administration would 'stand by them' as they protested against the country's leadership.

'To the brave, long-suffering people of Iran: I've stood with you since the beginning of my Presidency, and my Administration will continue to stand with you. We are following your protests closely, and are inspired by your courage.'

Protesters outside Amirkabir University in Tehran demanded the Ayatollah's resignation over the military disaster

Thousands gather outside Amir Kabir University on Saturday screaming 'Death to the Dictator'

Iranians shout slogans against the government in protests in Tehran Saturday night

Iran for days claimed that a technical failure caused the crash, before admitting on Saturday that its own surface-to-air missiles brought the plane down.

Iran was on high alert at the time, hours after launching ballistic missiles at U.S. forces in Iraq in a strike that caused no casualties. That missile strike was in retaliation for a U.S. operation that killed powerful Iranian General Qassem Soleimani

On Saturday afternoon, candlelight vigils at universities in Tehran for the victims of Flight 752 began to turn to protests against the regime. Large protests were reported at the universities of Tehran, Sharif Industrial, Amir Kabir, and Allameh.

At Amirkabir University, protesters chanted 'Down with the dictator' and 'shame on IRGC [Revolutionary Guard], let the country go.'

At Sharif University, crowds of outraged Iranians chanted 'commander in chief, resign!' The Ayatollah is Iran's commander in chief.

'Our enemy is right here; They lie when they say it's the US' protesters were heard chanting in one video.

'I now believe the word of the Great Satan,' one protester wrote in Persian on Twitter, apparently referring to the U.S. intelligence reports that blamed Iran for shooting the plane down, which the regime furiously denied at first.

A picture is seen on Saturday next to candles lit by people and families of the victims of the crash of Flight 752

Riot police with shields and batons massed to disrupt the anti-government protests on Saturday night

The regime quickly cracked down on the protests with tear gas and water cannons

Screams were heard as regime forces fired tear gas at the protesters in a brutal crackdown after night fell

A woman gestures during a protest against the government outside Amirkabir University in Tehran, Iran on Saturday

Iranians shout slogans against the government after a vigil held for the victims of the airplane of Ukrainian International Airlines that crashed near Imam Khomeini Airport turned into an anti-government protest outside Amirkabir University

Protesters demanded that those responsible for shooting down the civilian plane be publicly tried and held accountable.

The crowd also condemned the Islamic Republic's paramilitary internal security force, chanting 'Death to Basij.'

As night fell, riot police attempted to break up the protests with tear gas.

Cops armed with shields and batons tried to disperse the crowds, and police fired water canons into the crowds of protesters.

Anti-regime factions said that the protests reflected the frustrations of Iranian citizens with the government corruption and oppression.

'The protest by thousands of Iranians in Tehran burst the propaganda balloon of the regime regarding Qassem Soleimani's elimination,' said Shahin Gobadi, spokesman of the anti-regime group People's Mojahedin Organization of Iran, in a statement to DailyMail.com.

Gobadi said that the protests 'showed the true sentiments of the Iranians and once again clearly proved that Iran is a powder keg and the Iranian people will not stop until the regime change.'

Iranians light candles and hang flowers for victims of Ukraine International Airlines Boeing 737-800 during a protest in front of the Amir Kabir University. What began as a vigil for the dead turned to anti-government protests

Iranians protest against the government outside Amirkabir University in Tehran, Iran on Saturday

People gather for a candlelight vigil to remember the victims of the Ukraine plane crash, at the gate of Amri Kabir University that some of the victims of the crash were former students of, in Tehran, Iran on Saturday

At Amirkabir University, protesters chanted 'Down with the dictator' and 'shame on [Revolutionary Guard], let the country go'

Iranian Brigadier General Amirali Hajizadeh, the Guards' aerospace commander, said on Saturday a surface-to-air missile operator had mistaken the Boeing 737 for a U.S. cruise missile responding to Iranian ballistic missile attacks, and only had ten seconds to decide whether or not to open fire.

'I wish I had died, and I wouldn't have seen such an incident,' Hajizadeh said somberly at a press conference. He claimed that a 'request had been made to clear the sky from civil flights at that time, but it did not happen due to reservations.'

For days, Iran vehemently denied that it was responsible for downing Flight 752 from Tehran to Kyiv on January 8, accusing the U.S. of spreading malicious propaganda and lies for suggesting such a scenario.

Hajizadeh claimed that the country's top military leaders were not initially aware that their own air defense system had shot the plan down, leading to confusion. Now the country has come clean, but still blames 'US adventurism' for the fatal 'error'.

'The delay in releasing information was not aimed at hiding the issue but it is the routine drill that the General Staff should study the case (first); and all information was collected on Friday morning after studies and what had happened became clear then,' Hajizadeh said.

Iranian President Hassan Rouhani extended condolences to the families of those killed in the incident, and promised that those responsible would be prosecuted.

'The Islamic Republic of Iran deeply regrets this disastrous mistake... My thoughts and prayers go to all the mourning families. I offer my sincerest condolences,' Rouhani said in a statement on Saturday.

'I wish I had died, and I wouldn't have seen such an incident,' said a somber Brigadier General Amirali Hajizadeh, the Guards' aerospace commander, at a press conference. Iran admitted that it shot down Flight 752, thinking the plane was a missile

Ukraine International Airlines' Boeing 737-800 plane wreckage is seen in a picture from investigation team released today

Rescue workers at the crash site recovered the bodies of victims on Wednesday (above)

He said that 'the terrible catastrophe should be thoroughly investigated, and those responsible for this unforgivable mistake will definitely be identified and prosecuted'.

But the country's Foreign Minister Javad Zarif said 'US adventurism' was to blame for Iran shooting down the plane, a week after an American drone killed Iranian General Qassem Soleimani in Iraq.

Zarif wrote: 'A sad day. Preliminary conclusions of internal investigation by Armed Forces: Human error at time of crisis caused by US adventurism led to disaster.

'Our profound regrets, apologies and condolences to our people, to the families of all victims, and to other affected nations.'

Iran's supreme leader Ayatollah Seyed Ali Khamenei also offered condolences to the families, as he called for an investigation and ordered the military to address 'shortcomings' on Saturday morning.