LONDON — Ukraine and Russia are still at war. Since the Minsk II peace agreement came into effect on Feb. 15, nearly 400 Ukrainian soldiers and more than 200 civilians have been killed. Many more may die yet. As European Union leaders gather for a summit meeting this week, with the issue of whether to renew sanctions against Russia far from resolved, they cannot afford to ignore the continued violations of the cease-fire.

The Russian president, Vladimir V. Putin, got the better end of the deal in Minsk II. He forced Ukraine to accept as legitimate the authorities he installed in the territories invaded by Russia. He weighted the deal so as to ensure that the Ukrainian president, Petro O. Poroshenko, would come under pressure from both his political allies and enemies when Kiev honored its commitments. And he made Ukraine’s progress toward potential European Union membership a great deal more complicated.

For all of this, it is Mr. Putin who has done the least to ensure Minsk II remains in place.

He has demonstrated that he has the ability to stop and start the war in Ukraine when it suits him. In the first six months following the deal, the Organization for Security and Cooperation in Europe recorded daily violations — including not only small-arms fire, but the use of mortars, tanks and heavy artillery. Then, on Sept. 1, the war stopped — just as Russian forces began arriving in Syria.

For two months, there was, as the O.S.C.E. reported, “relative calm.” Then, in early November, hostilities resumed and there have been dozens of incidents daily. The Russia-backed separatist forces have escalated the conflict again.