US president Joe Biden’s last-gasp decision to permit Ukraine to fire western-made, long-range missiles at military targets deep inside Russian territory runs the risk of triggering a sharp increase in retaliatory sabotage, such as cyber and arson attacks on Britain and its European Nato partners. Vladimir Putin, who ordered the full-scale, illegal invasion of Ukraine 1,000 days ago tomorrow, has long warned that Kyiv’s expanded use of US-, British- and French-made missiles would be viewed by Moscow as an act of war by Nato, and could trigger catastrophic consequences. Now Putin’s bluff, if it is a bluff, is being called. Much the same may be said of Keir Starmer and the EU. A joint statement by G7 leaders, coinciding with the 1,000-day landmark, pledged “unwavering support for Ukraine for as long as it takes”. Starmer reiterated that commitment en route to this week’s G20 summit in Brazil. Exactly what it means in practice may soon be harshly tested. Biden’s decision is welcome, if overdue. Amid grinding Russian ground advances, EU feuding and Donald Trump’s unpropitious re-election, the war has reached a critical juncture, militarily and diplomatically. The outcome is in the balance as the scales momentarily tip towards more death and destruction, then back towards some form of Trump-imposed land-for-peace sell-out. Russia has the advantage at present. But Kyiv will not and must not give up. Biden was slow to give the missile go-ahead, despite months of pressure from President Volodymyr Zelenskyy, who has argued, with good reason, that Ukraine is fighting with one hand tied behind its back. Russian airfields, military bases and command centres that are used to mount almost daily, lethal missile and drone attacks on Ukraine’s cities and energy infrastructure are out of range. Biden’s tardiness was the product of an excessive caution that has seen the US drag its feet on supplying new weapons from the start. If Ukraine had been armed in 2022 with all the tanks, air-defence systems, missiles and fighter aircraft it has subsequently, belatedly been given, it might not be struggling as it is now. But his hesitation was reportedly reinforced by a recent classified US intelligence assessment. It warned that Putin could respond to the use of the US long-range army tactical missile system (Atacms), and the similarly capable Anglo-French Storm Shadow missiles, AKA Scalp-EG, on Russian soil, with attacks on the US and its allies. Direct, overt Russian armed retaliation against European military bases or territory seems unlikely, although tensions with Poland and other “frontline” Nato countries are running high. Dark threats by Putin cronies such as former president Dmitry Medvedev about using nuclear weapons are dismissed as rhetorical fearmongering. Instead, the intelligence finding suggested, Russia may step up covert, deniable sabotage: cyber, infowar and arson attacks of the type it has undertaken in recent years. This would allow the Kremlin to impose a cost, especially on wavering Nato members such as Olaf Scholz’s Germany, while avoiding all-out east-west war. The GRU, Russia’s military intelligence agency, and other state organs are said to have been tasked by Putin with preparing asymmetrical responses for exactly the circumstances that are now unfolding. The overall aim: to alarm and disrupt western societies and publics. The GRU is notorious in Britain for carrying out the non-Ukraine-related Salisbury poisonings in 2018. In March this year, it was linked to arson at a warehouse in east London supposedly used to supply Ukraine. Attacks on a factory in Poland and non-military targets in Latvia and Lithuania are also attributed to the GRU. In May, Donald Tusk, Poland’s prime minister, said 12 people had been arrested for beatings, arson and “acts of sabotage on commission from Russian intelligence services”. These may have been mere practice runs. Kaja Kallas, former prime minister of Estonia and newly nominated EU foreign policy chief, says Moscow is waging a “shadow war” on Europe. Norway’s prime minister, Jonas Gahr Støre, warns that Russia may target energy producers and arms factories. Europe needed a coordinated approach, Kallas said. “How far do we let them go on our soil?” Nor is the threat confined to land. Last week, in the latest in a series of incidents, a Russian spy ship – officially classed as an “oceanographic research vessel” – was militarily escorted out of the Irish Sea. Its unexplained presence there and around UK coasts has renewed concerns about the security of critical undersea infrastructure, including pipelines and internet cables linking the UK, Ireland, Europe and the US. Described as the latest attempt to probe western defences and vulnerabilities, the incident followed an investigation in Nordic countries last year into suspected Russian state-led espionage ops. Spy ships disguised as fishing vessels were being used to plan future attacks on windfarms and communications cables in the North Sea, it said. However Russia responds – and the initial Kremlin reaction on Monday was wait-and-see – Biden’s decision challenges Ukraine and the European Nato allies, too. Having pressed so hard for so long, Zelenskyy must prove that the missiles make a difference. US officials are sceptical they can change the course of the war. EU officials in Brussels hope they will. What Biden appears to hope is that long-range strikes on North Korean troops newly deployed in Russia’s contested Kursk region will deter Pyongyang from further involvement. That seems improbable, too. Kim Jong-un, North Korea’s ostracised dictator, is Putin’s new best bro. He’s not noted for a caring attitude to human life. With Trump’s advisers threatening a de facto betrayal of Ukraine, Europe’s leaders, including Starmer, must put their money, lots of it, and their weapons where their mouths are – and help Zelenskyy maintain the fight, even without US hardware and financial backing, if need be. The problem is that unity of purpose, and resources, are lacking. Scholz broke with most of the EU last week when he phoned Putin for a chat. The chancellor (who continues to refuse to supply Germany’s Taurus long-range missiles to Kyiv) said he was pursuing peace. But it looked like weakness with snap elections brewing, and it angered other leaders. “No one will stop Putin with phone calls,” Tusk snarled. “Telephone diplomacy cannot replace real support from the whole west for Ukraine.” The “whole west” means France, too. But President Emmanuel Macron, having spoken frequently and passionately about the vital importance for Europe of defeating Russia, now appears to be temporising about actually letting Kyiv fire French missiles. Will Starmer give a green light, or will he also get cold feet? With Ukraine burning, Europe divided, and Biden two months away from oblivion, it’s little wonder that Putin, with a host of dirty tricks up his sleeve, thinks he’s winning the Ukraine missile crisis. Simon Tisdall is the Observer’s foreign affairs commentator