Jeremy Corbyn, the Labour leadership candidate, wrote a letter of support for a vicar who was banned from social media after suggesting that Israel was responsible for the 9/11 attack on the twin towers.

The Reverend Stephen Sizer used his internet accounts to spread ideas which were ‘clearly anti-Semitic’, the Church of England said. He was banned by Church authorities for six months in February.

Corbyn argued that Sizer was 'under attack' by a pro-Israeli smear campaign.

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Jeremy Corbyn (left) supported Stephen Sizer (right) when he was banned from social media after promoting anti-Semitic material online. Corbyn argued that Sizer had been smeared for his anti-Israel views

Stephen Sizer meets Nabil Kaouk, a top Hezbollah official and militant commander, in Lebanon

Stephen Sizer meets Zahra Mostafavi, the daughter of Ayatollah Khomeini, in Iran

The controversy arose in February after the vicar posted an article on his Facebook page which attempted to connect wealthy Jews to the 9/11 attacks. ‘Is this antisemitic?’ Mr Sizer commented under the link, adding ‘It raises so many questions.’

The Bishop of Guildford, the Right Reverend Andrew Watson, said that the vicar’s campaigning on the Middle East was ‘no longer compatible with his ministry as a parish priest.’

The bishop said: ‘By associating with or promoting subject matter, which is either ambiguous in its motivation, or, worse still, openly racist, he has crossed a serious line. I regard these actions as indefensible.’

He conceded, however, that 'I do not believe that his motives are anti-Semitic; but I have concluded that, at the very least, he has demonstrated appallingly poor judgment in the material he has chosen to disseminate, particularly via social media, some of which is clearly anti-Semitic.'

Corbyn wrote to the Church authorities at the time, suggesting that Sizer had been victimised because he had 'dared to speak out against Zionism'.

'Reverend Stephen Sizer seems to have come under attack by certain individuals intent on discrediting the excellent work that Stephen does in highlighting the injustices of the Palestinian Israeli situation,' Corbyn wrote.

He also blamed Sizer's actions on the vicissitudes of the internet.

'The internet is a complicated piece of technology and with the best will in the world, imperfect links are made and one would have to spend 8 hours a day “surfing” the net just to be 100% certain one’s views to not become contaminated in any way at all,' he wrote. 'Even then, connections can inadvertently be made.'

This was far from the only instance that Sizer has been accused of anti-Semitism.

In 2014, the vicar flew to Iran to attend a 'New Horizons' conference intended to 'unveil the secrets behind the dominance of the Zionist lobby over US and EU politics', and delivered a speech on the 'Israeli lobby'.

The conference, which was hosted by the Iranian regime, attracted a number of alleged Holocaust deniers and conspiracy theorists. The French comedian Dieudonne M'Bala M'Bala, whose 'quenelle' gesture was judged to be anti-Semitic, reportedly attended.

One session was devoted to examining 'Mossad’s role in the 9/11 Coup d’Etat', and another examined '9/11 and the Holocaust as pro-Zionist public myths'.

Sizer has also appeared frequently on a Hezbollah television channel called Al Etejah. In a programme called 'Enlightenment: Escaping Auschwitz', Sizer said: 'Israel can get away with it because they trade on the Holocaust'.

He has also toured South Lebanon, and was pictured (above) apparently meeting Nabil Kaouk, a top Hezbollah official and militant commander. He also was photographed (above) meeting Zahra Mostafavi, the daughter of Ayatollah Khomeini, in Iran.

Bizarrely, Sizer also appeared in a 2014 promotional video for the Syrian tourist board, in which he praised the Assad regime and blamed the unrest in the country on 'foreign interference'.

Sizer told MailOnline, 'I have been asked by my Bishop not to engage in public comment for the foreseeable future as a result of media controversy surrounding my alleged views on Israel and Iran.'

When contacted by MailOnline, Corbyn was unavailable for comment.

Corbyn's support for Sizer raises serious questions about the Labour contender's judgment, following the emergence of a video (above) in which he described Hamas and Hezbollah as his 'friends'.

Concerns have been mounting since MailOnline revealed that Paul Eisen, the self-professed Holocaust denier, gave Corbyn his support in an extraordinary blog post in which he said that he has been close to the Labour leadership contender for more than 15 years.

Eisen, who runs a pro-Palestinian pressure group, also claimed the Islington North MP attended 'every single' one of his annual anti-Israel events and has even donated to the group, Deir Yassin Remembered (DYR).

'One evening 15 years ago I cycled over to see [Corbyn],' he wrote. 'I was just beginning to establish Deir Yassin Remembered in the UK and I wanted him to join.

'I'd hardly begun my feverishly-rehearsed pitch before his cheque book was on the table.

'From that day on, without fuss or bother, whether DYR was flavour-of-the-month or the maggot-at-the-bottom-of-the-food-chain, he attended every single Deir Yassin commemoration.'

Paul Eisen, left, is a self-professed Holocaust denier who frequently shares anti-Semitic and far-Right content on his blog. Jeremy Corbyn, right, who according to Eisen has attended 'every single' one of his organisation's annual events, appears to sit attentively during one such meeting in St John's Wood Church in 2013

DYR focuses on controversial allegations that Jewish soldiers killed about 100 Arab villagers in the run-up to the war of 1948, and seeks to promote its remembrance at annual events.

It highlights the fact that the village of Deir Yassin is situated close to Yad Vashem, Israel's Holocaust museum.

Many mainstream Palestinian activists view the group as anti-Semitic and in thrall to 'anti-Semitic conspiracy theories'.

In 2007, the Palestinian Solidarity Campaign proposed a motion disowning Eisen's group, stating that 'membership or participation in DYR is incompatible with being a member of Palestinian Solidarity Campaign. You cannot oppose racism against the Palestinians and turn a blind eye to anti-Semitism.'

The DYR website contains a picture appearing to show Corbyn attending one of the organisation's event in 2013 (above).

Politicians need not only to condemn antisemitism but be seen to distance themselves from it Jonathan Sacerdoti, Campaign Against Antisemitism Jonathan Sacerdoti, Campaign Against Antisemitism

Eisen's open Holocaust denial has made him a toxic figure among many pro-Palestinian activists.

'I question that there ever was an official plan on the part of Hitler or any other part of the National Socialist Regime systematically and physically to eliminate every Jew in Europe,' Eisen has written on his blog.

'I question that there ever existed homicidal gas-chambers… Deny the Holocaust! For my money, a child of six can see that something's not right about the Holocaust narrative... For me, "Holocaust Denier" is a label I accept.'

The alleged relationship with Eisen will be particularly embarrassing for the Labour leadership contender as the Holocaust denier believes Corbyn stood by him when he felt ostracised.

On his blog, Eisen recalls a period when he felt 'despised' by mainstream society, and only Corbyn refused to shun him.

'During the time when I felt so marginalised and isolated, when the movement with which he was associated so despised me, Jeremy always said hello,' he wrote.

A spokesperson for Jeremy Corbyn's campaign said:

'Paul Eisen is not someone Jeremy Corbyn's office has any dealings with. Based upon what is in written in the articles here, anyone can call themselves a “long time associate” when in fact that is not the case. Paul Eisen clearly holds some of the most extreme views that are entirely his, and Jeremy totally opposes them and disassociates himself from them.'

When asked to confirm whether Corbyn knows Eisen personally, or whether Eisen's accounts of Corbyn attending 'every single' one of his events and 'opening his cheque book' to his organisation are correct, the spokesperson declined to comment.

Popular: Jeremy Corbyn sits on a stage surrounded by members of the Labour party in Bradford

Rhetoric: Jeremy Corbyn makes a speech in Bradford amid revelations that he has 'links' to a notorious Holocaust denier

Supported: Jeremy Corbyn arrives in Bradford to give a speech to Labour voters

Eisen is also a supporter of David Duke, the former Ku Klux Klan grand wizard, 9/11 'truther' and notorious conspiracy theorist.

When promoting a Duke video entitled The Zionist Red Army on his website, Eisen wrote: 'Oh, how I wish I could stop posting David Duke (it gets me into no end of trouble). Trouble is, he just will not stop telling the truth.'

The video in question includes an extended anti-Semitic rant by Duke. Towards the end, he says: 'The people of Europe and America, [the Jews are] coming for you… Together we will defeat the true apostles of hate'.

Eisen also promotes articles from a prominent White Supremacist website on his blog. One of these, posted in March, refers to Jews as 'rats' and talks of the 'battle we wage' against 'international Jewry'.

Jonathan Sacerdoti, Director of Communications at the Campaign Against Antisemitism, said:

'No politician should have any association whatsoever with a Holocaust denier like Paul Eisen. It is disturbing to see these pictures of a potential Leader of the Opposition at one of his events.

'Politicians need not only to condemn antisemitism but be seen to distance themselves from it.'

Eisen could not be reached for comment.

These latest revelations raise serious questions about Corbyn's association with extremists of all stripes. On Thursday,Corbyn refused five times to condemn IRA atrocities when interviewed by BBC Radio Ulster.