There is never a good time to stir tensions in the Middle East. Yet, in the midst of the Covid-19 pandemic, with a delicate transition of power under way in the United States and Israeli politics dysfunctional, someone gave the order to kill Iran’s top nuclear scientist. The Iranian leadership has not overreacted, warning rather than seeking revenge against those it suspects with a military response. Whoever gave the go-ahead is risking unleashing war in one of the world’s most unstable regions; restraint and diplomacy are now needed. No one has claimed responsibility for the shooting of Mohsen Fakhrizadeh in an ambush by unidentified gunmen near Tehran last Friday, but Israel and the US are the main suspects. Both claimed he had been the driving force behind Iran’s efforts to produce nuclear weapons, even though Tehran announced it had abandoned such a programme in 2003. Israeli Prime Minister Benjamin Netanyahu said two years ago that the scientist’s name should be remembered, in effect confirming suspicions Israel had a blacklist and its agents were behind a series of killings of Iranian nuclear experts. Outgoing US President Donald Trump and his administration are also supportive of Netanyahu and avowedly anti-Iranian; the assassination came 10 months after an American drone killed Iran’s top spymaster in Iraq. There is no denying Trump’s efforts to derail the international endeavour to curb Iran’s nuclear proliferation. His withdrawal of the United States from the deal and reimposition of harsh sanctions has jeopardised the agreement signed in 2015 with China, Russia and their European partners. US president-elect Joe Biden has vowed to rejoin the pact, but he does not take office until January 20, giving the Trump administration a free hand to make it even more difficult to repair the damage. Fakhrizadeh’s killing could easily prompt Iran to take rash action, sparking war with rivals, which may deepen animosity between Washington and Tehran, or strengthen hardline factions in Iran trying to prevent diplomacy with the West. Trump’s Middle East envoy, son-in-law Jared Kushner, is on a trip to the region, his first stop being in Saudi Arabia, Iran’s avowed enemy. Reckless decisions have to be avoided. There is every need for restraint.