A pro-Brexit campaign has sparked a furious reaction after attempting to link the killing of 49 people at a gay US nightclub and the EU referendum debate.

Featuring an image of what appear to be Isis militants brandishing guns in a desert, a post on the official Twitter account of the Leave.EU campaign carried the warning: “Islamist terrorism is a real threat to our way of life. Act now before we see an Orlando-style atrocity here before too long.”

It was immediately denounced as "shameful" by Cabinet minister Nicky Morgan, while Will Straw, the director of Britain Stronger in Europe, labelled it “Trump-ist scaremongering”.

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It comes after 50 people including the gunman were killed and 53 were wounded when 29-year-old Omar Mir Seddique Mateen opened fire at Pulse nightclub in Orlando.

The Leave.EU poster was attached to a tweet which claimed: "The free movement of Kalashnikovs in Europe helps terrorists. Vote for greater security on June 23. Vote Leave."

Within minutes of the post's appearance, pro-Remain Education Secretary Ms Morgan responded: “This is really shameful”.

The Education Secretary added: "Using the tragic deaths of innocent people to make a political point is simply shameful. Leave.EU must apologise for the hurt they have caused and apologise immediately.

“And Vote Leave need to condemn such despicable tactics and make clear that the Orlando attack has nothing whatsoever to do with the EU debate in this country”.

Labour’s shadow Foreign Secretary Hilary Benn said the image was “shameful and cowardly”. He added: “It takes courage to stand by your principles and your friends when they are attacked, whether in Orlando, Paris or Brussels.

In pictures: Orlando nightclub shooting Show all 30 1 /30 In pictures: Orlando nightclub shooting In pictures: Orlando nightclub shooting Friends and family grieve after a list of hospitalised victims was released, implying the death of those who weren't on the list and hadn't been heard from, outside a Hampton Inn & Suites hotel near the Orlando Regional Medical Center AP In pictures: Orlando nightclub shooting People mourning for victims of the mass shooting near the Pulse gay nightclub in Orlando AFP/Getty Images In pictures: Orlando nightclub shooting Mina Justice speaks to a reporter discussing texting with her son Eddie who was in a bathroom at Club Pulse in Orlando. It has now been confirmed that Eddie Justice was among the 50 people killed in the massacre AP In pictures: Orlando nightclub shooting FBI agents investigate near the damaged rear wall of the Pulse Nightclub Getty Images In pictures: Orlando nightclub shooting Terry DeCarlo, executive director of the LGBT Center of Central Florida (C) is comforted by Orlando City Commissioner Patty Sheehan (R) after a shooting involving multiple fatalities at a nightclub in Orlando AP In pictures: Orlando nightclub shooting FBI agents investigate the damaged rear wall of the Pulse Nightclub Getty Images In pictures: Orlando nightclub shooting Police officials investigate the back of the Pulse nightclub after a shooting involving multiple fatalities at the nightclub in Orlando AP In pictures: Orlando nightclub shooting A member of the Medical Examiners office wheels a body to a vehicle from the mass shooting at Pulse Nightclub Getty Images In pictures: Orlando nightclub shooting A photograph posted by the Orlando Police Department on Twitter with the words, "Pulse shooting: In hail of gunfire in which suspect was killed, OPD officer was hit. Kevlar helmet saved his life", in reference to the operation against a gun man inside Pulse night club in Orlando REUTERS In pictures: Orlando nightclub shooting FBI, Orlando Police Department and the Orange County Sheriff's Office personnel investigate the attack at the Pulse nightclub in Orlando AP In pictures: Orlando nightclub shooting Annette Stubbs, a pastor at a local church, prays for victims a few blocks from a crime scene at the nightclub where a mass shooting took place AP In pictures: Orlando nightclub shooting Aimee McCarthy from Jacksonville, gives blood at the oneblood facility, to help the victims from a mass shooting at a nightclub in Orlando AP In pictures: Orlando nightclub shooting Police forensics investigators work at the crime scene of a mass shooting at the Pulse gay night club in Orlando REUTERS In pictures: Orlando nightclub shooting An injured person is escorted out of the Pulse nightclub after a shooting rampage AP In pictures: Orlando nightclub shooting An injured man is escorted out of the Pulse nightclub after a shooting rampage AP In pictures: Orlando nightclub shooting An injured man is escorted out of the Pulse nightclub after a shooting rampage AP In pictures: Orlando nightclub shooting Law enforcement officials work at the Pulse nightclub following a fatal shooting AP In pictures: Orlando nightclub shooting Orlando Police officers direct family members away from the nightclub AP In pictures: Orlando nightclub shooting The scene outside the Orlando gay club where multiple people have been shot AFP/Getty Images In pictures: Orlando nightclub shooting The injured are treated in the street outside Pulse in Orlando following the shooting EPA/Univision In pictures: Orlando nightclub shooting Two witnesses, Jermain Towns (left) and Brandon Shuford, wait down the street for news following shooting and hostage stand-off at the Pulse nightclub. Mr Towns said his brother was in the club at the time AP In pictures: Orlando nightclub shooting Emergency services at the scene. Ambulance crews and firefighters were outside the club alongside police. EPA In pictures: Orlando nightclub shooting People treating the wounded on the street EPA In pictures: Orlando nightclub shooting Friends and family members embrace outside the Orlando Police Headquarters during the investigation of a shooting at the Pulse night club Reuters In pictures: Orlando nightclub shooting Law enforcement agencies and local city representatives give a news conference in the wake of a mass-casualty shooting at the Pulse nightclub in Orlando Rex In pictures: Orlando nightclub shooting Orlando police officers seen outside of Pulse nightclub after a fatal shooting and hostage situation in Orlando, Florida Getty In pictures: Orlando nightclub shooting Friends and family console one another outside the Orlando Police Headquarters In pictures: Orlando nightclub shooting U.S. President Barack Obama speaks about the worst mass shooting in U.S. history that took place in Orlando REUTERS In pictures: Orlando nightclub shooting Imam Syed Shafeeq Rahman, the Imam of the mosqe that mass shooter Omar Mateen attended, speaks to the media in Fort Pierce. The imam said that the suspect never gave any indication he was capable of such violence.Omar Mateen attended evening prayers three or four times a week at the Islamic Center of Fort Pierce, bringing his son who is about four or five years old AFP/Getty Images In pictures: Orlando nightclub shooting Omar Mateen has killed 50 people at a gay nightclub after pledging allegiance to Isis in the deadliest mass shooting in US history Myspace

“Doing so makes us stronger and shows our resolve to stand up for our values and our way of life in the face of those who hold both in such murderous contempt.”

Iain Duncan Smith said that Vote Leave – the official Brexit campaign – had “nothing to do with that organisation” when asked about the controversial image posted by Leave.EU.

Mr Duncan Smith, the leading Brexit campaigner and former Work and Pensions Secretary, told BBC Radio 4's The World at One programme: “All I would say to you is that Europol has made the point to the Home Secretary quite recently that unless we control migration there are threats to security, that's a fact of life, but I'm not going to get involved in peculiar tweets that go out from other organisations that I don't sign up to.”

Asked if he condemned the comments, he replied: “I think it is completely pointless to try and make something out of what is a tragedy in America.

“It has nothing to do with this debate at all, and I abhor anybody who tries to make capital out of that.”

The Independent was unable to contact Leave.EU - which has since deleted the post - for a comment.