"Undoubtedly the Islamic Republic of Iran will not ignore this crime. It is absolutely clear for us who did that, what group they are and with whom they are affiliated," Iranian President Hassan Rouhani warned before leaving for New York for the United Nations General Assembly. "All of those small mercenary countries that we see in this region are backed by America. It is Americans who instigate them and provide them with necessary means to commit these crimes." Iran's President Hassan Rouhani speaks at a military parade marking the 38th anniversary of Iraq's 1980 invasion of Iran on Saturday. Credit:AP Rouhani is a relative moderate who was elected twice on promises to improve relations with West, and who signed the 2015 nuclear agreement. At the UN General Assembly that year, he declared that "a new chapter had started in Iran's relations with the world". "For the first time, two sides rather than negotiating peace after war, engaged in dialogue and understanding before the eruption of conflict." An eruption now seems more likely. What changed in the meantime seems to be the politics of the region and the US. While America's Sunni Gulf Arab allies in the region criticised the nuclear deal, many later acknowledged that it did what it was designed to do.

Iran limited its enrichment of uranium, making it virtually impossible for it to quickly develop nuclear weapons, something the government insists it has never sought. In exchange, some international sanctions were lifted, allowing Iran to rejoin the global financial system and sell its crude oil to American allies. Over time, however, Gulf states adopted an increasingly harder tone with Iran. Officials in Tehran point to comments by Saudi Crown Prince Mohammed bin Salman, now next in line to the throne in Iran's Mid-east arch-rival. "We know we are a main target of Iran," Prince Mohammed said in a 2017 interview, shortly before becoming crown prince. "We are not waiting until there becomes a battle in Saudi Arabia, so we will work so that it becomes a battle for them in Iran and not in Saudi Arabia." Rudy Giuliani, an attorney for President Donald Trump, speaks at the Iran Freedom Convention for Human Rights and democracy in Washington in May. Credit:AP He did not elaborate, though the kingdom and its allies were mired then as they are now - in a war in Yemen against Iran-aligned Shiite rebels. While Iran denies arming the rebels, known as Houthis, UN investigators, analysts and Western nations all say Tehran supplies weapons ranging from assault rifles to the ballistic missiles, which have been fired deep into Saudi territory.

After Prince Mohammed's comments last year, Saudi-aligned satellite news channels began playing up stories about Iranian opposition and exile groups. They also began publicising the nighttime pipeline attacks by Arab separatists in Khuzestan, Iran's oil-rich southwestern province, which Iraqi dictator Saddam Hussein tried to seize in his 1980s war with Iran. Those separatists claimed responsibility for Saturday's attack in Ahvaz, Khuzestan's capital, which struck one of many parades in the country marking the start of the 1980s war. Iranian officials, who blame the separatists for the attack, say the militants wore military uniforms and hid their weapons along the parade route ahead of time - showing a level of sophistication previously unseen by the separatists. A woman takes her children to shelter as an army member tries to help them, during a shooting at a military parade marking the 38th anniversary of Iraq's 1980 invasion of Iran on Saturday. Credit:AP There has been no direct evidence linking the separatists to Saudi Arabia. However, Iranian officials have seized on the fact the separatists immediately made their claim of responsibility on a Saudi-linked, Farsi-language satellite news channel based in Britain. Loading

The United States has meanwhile been ramping up pressure on Iran since Trump withdrew from the nuclear agreement in May, restoring crippling sanctions and voicing support for anti-government protests fuelled by economic woes. The Trump administration has said its actions aren't aimed at toppling Iran's government. But in the meantime, Giuliani has continued speaking before meetings of an exiled Iranian opposition group. Before being appointed national security adviser earlier this year, John Bolton gave impassioned speeches calling for regime change. "The declared policy of the United States of America should be the overthrow of the mullahs' regime in Tehran," Bolton told Iranian exiles in July 2017. "The behaviour and the objectives of the regime are not going to change, and therefore, the only solution is to change the regime itself. He added, to cheers: "And that's why before 2019, we here will celebrate in Tehran."