In the past few days, Vladimir Putin’s objectives in eastern Ukraine have taken a new and darker turn. The Russian president has so far been opportunistic in his conduct of the war with Kiev, keeping open his options to escalate and de-escalate where and when he sees fit. Now, pro-Russian rebels are engaged in a major offensive against the Ukrainian army on several fronts.

There can be no doubt that this surge in fighting is at the behest of the Russian leader. Since the start of this year, Nato has observed hundreds of pieces of military equipment crossing the untended Russia-Ukraine border into the hands of the separatists — including rocket launchers, tanks and armoured vehicles. Many believe Mr Putin is trying to carve a viable puppet state out of Ukraine. This poses a new challenge for the US and EU and raises the question of whether the west should arm the Ukrainian military.

Up till now, the west has employed sanctions and diplomacy in a bid to force Mr Putin to draw back. Sanctions have hurt the Kremlin and deepened Russia’s economic crisis. But nothing has yet deterred Mr Putin from probing both Kiev’s defences and the west’s resolve.