After a brief winter lull, fighting has returned to Ukraine. The past week has seen the renewal of the conflict that has ebbed and flowed around the airport at Donetsk ever since the signing of the Minsk peace agreement between Kiev, Moscow and the Russia-backed rebels last September.

The booming of artillery never really died down along the so-called demarcation line between Ukrainian and rebel forces agreed at Minsk. Both sides have tried to grab territory around that line to strengthen their strategic positions. But recent days have seen an ominous increase in both the tempo and violence of military operations.
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In swift succession, a rebel offensive designed to force the Ukrainian defenders to withdraw from large parts of the airport complex has been followed by a fierce Ukrainian counterthrust. Kiev has claimed that 1,000 Russian troops have crossed the border to assist their rebel clients. Moscow has vigorously denied this, while warning Kiev ominously of the futility of seeking “military solutions” to the crisis.

With casualties mounting on both sides, the Minsk deal is in danger of collapse, plunging Ukraine back into full-blown war, as bloody as it is senseless.

Mr Putin bears most responsibility for the instability. Moscow has not fulfilled key elements of the Minsk accord, even as the Russian president has claimed co-authorship of the document. Russia has failed, above all, to implement a provision to allow Ukraine to regain full control of its international border with Russia — which in turn would enable Kiev to stop the flow of men and weapons across what remains an untended frontier.

All parties, including the west, must continue to press for full implementation of the Minsk accords. European nations, in particular, need to be at one on this. Now is no time to flirt with concessions to the sanctions regime. Thankfully, EU foreign ministers – even from countries that favoured greater appeasement of Russia – disavowed proposals from Federica Mogherini, the EU’s new foreign policy chief, that hinted at softening the EU line.

The correct stance must be a mixture of carrot and stick. The EU and the US should press Moscow to implement the Minsk bargain, while making clear that the latest round of sanctions imposed in September could be rolled back in the event of prompt compliance. Moscow has strong incentives to do so, since these sanctions — which restricted Russian banks and oil companies’ access to western financing — have combined with the plunge in oil prices to throw the economy into crisis.

Angela Merkel, the German chancellor, is right to insist that she will not participate in a mooted summit with the Russian and Ukrainian leaders in Kazakhstan unless Moscow demonstrates its bona fides. There should be no question of earlier sanction rounds being eased when they are reviewed in March unless Moscow changes tack.

Meanwhile, Petro Poroshenko, Ukraine’s president, must not allow himself to be drawn into an unwinnable conflict. Painful as it is politically, he must continue to push Mr Putin in joint efforts to reduce tension.

Since Russia’s response to the Maidan revolution plunged Ukraine into crisis, the outlines of a resolution have been clear. Kiev should implement a degree of decentralisation that gives Russophone communities some autonomy without dismantling the state. In past months Mr Poroshenko has gone some way to honouring his end of the deal, while Mr Putin has not. The Russian leader must be frank about his intentions. His present course leads nowhere, other than to further confrontation in Ukraine.