Tensions between the embittered neighbours have been running especially high since Russia accused Ukraine of attempting a terrorist attack in Crimea earlier this month. Vladimir Putin, Russia’s president, has since promised ominously ambiguous counter-measures, suggested that peace negotiations led by Germany and France were “senseless”, and flexed the muscles of Russia’s Black Sea fleet in exercises. Clashes along the line of contact in eastern Ukraine have become more frequent. Western officials have urged calm. Petro Poroshenko, Ukraine’s president, has threatened a new wave of military mobilisation. Yet few think the Kremlin is preparing for a(nother) major invasion, which would be costly in blood and treasure. Rather, the escalation seems aimed at diplomacy around the G20 summit on September 4th: by turning up the heat, Mr Putin hopes to extract more concessions from Ukraine and its distracted Western partners. The coming week will show how hot he wants things to get.