John Kerry, US secretary of state, has long enjoyed a reputation for being an indefatigable diplomat, engaging in shuttle diplomacy over the Iranian nuclear programme and the Middle East peace process. But few of his initiatives have prompted as much surprise as his recent visit to President Vladimir Putin in the Russian resort of Sochi.

Coming at a moment of acute tension in east-west relations over the Kremlin’s aggression in Ukraine, the four hours of meetings between the two have been criticised by some in the US as a sign that the White House is buckling. This would be the wrong judgment to make. The US should maintain its robust stance over Mr Putin’s attempts to destabilise Ukraine, but that should not stop Washington trying to engage directly with him if it can.

Eighteen months after the Ukraine crisis erupted, the west must remain on guard over Mr Putin’s intentions towards his neighbour. Although a ceasefire between the Kiev government and Russian-backed rebels was signed in Minsk in February, the guns in eastern Ukraine can still be heard in places. Victoria Nuland, US assistant secretary of state, said last week that Russian forces continue to violate the ceasefire “on a daily basis”. The political elements of the Minsk agreement, including the requirement that Kiev should decentralise powers to the rebel-held regions, and that Russia and its proxies return control of the international border to Ukraine, are yet to be implemented. But the current lull in fighting has created an opportunity for diplomatic dialogue that the US should exploit.