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.

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.