If you ever get the chance, go to Iran. It's a stunning country, with a rich history, hospitable people, and limitless culture. Though it lacks the jaw-dropping beauty of Esfahan or the history of Khorramabad, Tehran has a certain charm in its hustle-bustle.

Behind one of the many parks that litter the city, you might stumble across the Ministry of Foreign Affairs. It's drab and utilitarian, like countless government buildings the world over. Which makes the gargantuan billboard on the front lawn all the more extraordinary. The board depicts a blue and white Star of David, a phalanx of rockets, explosions, and three words, in English and Farsi, emblazoned across the length of it: "Death to Israel."

It would be comically surreal in another circumstance, not out of place in a Sacha Baron Cohen film. But that billboard represents the true face of the government in Iran.

It should be a stark reminder to the P5+1 powers en route to nuclear negotiations in Vienna next week that the Iranian regime is ideologically committed to the destruction of the state of Israel. Whatever failures Israel has as a state – and many Israelis would be happy to point them out – Israel remains a key ally in the heart of the Middle East to almost every country in the West. Israel cooperates closely with the US, UK and others on security and intelligence matters. We share the values of democracy, the rule of law and libertarianism.

President Obama has dispatched Secretary Kerry to the nuclear talks, blinded by two factors. First, Obama is desperate for his first major foreign policy victory since the successful assassination of Osama bin Laden. Hammered in the midterms, the Carter-esque labels of "weak" and "indecisive" are beginning to stick to the president.

His backtracking on American red-lines on Syrian chemical weapons, his uncertainty over facing up to President Putin's aggression in Crimea and Ukraine, and the failure of his attempt to broker peace in the Middle East have all contributed to the sense that President Obama is too calculating, too timid, too detached to sit in the Oval Office. He has precious little political capital left, and if he is to have the strength to push through his immigration reforms by executive order alone, he needs a policy victory fast.

Second, the president is gambling that he can kill two birds with one stone. Not only would a deal with Iran give him political capital at home, but America would secure the support of Iran in its war against the Islamic State. Iran, a powerful Shia state, would bring its considerable militarism to bear against Sunni fundamentalists threatening the stability of the entire region.

An exercise in short-termism

John Kerry was clear what the primary threat was when he told a foreign policy forum on Monday [17 November]: "If we don't defeat [the Islamic State] there will be no future for the Middle East." IS has indeed shown remarkable, brutal, resourcefulness. But to label them the greatest threat to the region is an exercise in short-termism.

The US and the U.K. are convinced that "the enemy of my enemy is my friend", but we should not sign a deal with Iran in the belief that it will create a shortcut to defeating IS.

For once, Prime Minister Netanyahu was correct in his assessment: "Don't fall for Iran's ruse. They are not your partner. They are not your friend." The Iranian regime, along with its puppets Assad and Hezbollah, will continue to create havoc and murder civilians long after IS has ceased to exist, or evolved into a new entity.

Iran has been sponsoring terrorism around the world for decades, and it continues to do so. Iran funds, trains and recruits for terrorist organisations across the world, including Hezbollah. Last year, Amnesty International estimates that the regime executed over 600 men, women and children. Public flogging and amputations have increased. Iran may have a friendly public face in President Rohani, but the character of the regime has not changed. Our flirtation with this regime is the worst of diplomatic hypocrisy.

But Obama needs his foreign policy victory. Our generals are looking for all the help they can muster against IS. Russia is now the pantomime villain. Ironically, it could be that the Republicans, who have caused so much damage in the Middle East in recent times, will be the ones to prevent an agreement with Iran by refusing to alleviate sanctions.

But for any of those diplomats, Democratic congressmen or British MPs who are considering making a deal with the devil, that billboard still stands proud outside the MFA building in Tehran. With "Death to Israel" emblazoned across it... in English.

Ross Cypher-Burley is a former spokesman for the British ambassador to Israel, and now works for strategic communications firm Portland. You can follow him on Twitter here.