Tensions between Russia and Ukraine are continuing to rise after an incident was reported over the weekend in which an attempted group of infiltrators from Ukraine entered Crimea, killing a Russian soldier and a member of their FSB security service. Russia has blamed the Ukrainian government’s spy agency, calling it a prelude to terror attacks on key infrastructure.

Residents reported yesterday that Ukraine had begun massing soldiers along the Crimean border, and today President Petro Poroshenko reported that he had placed the army on “combat alert” over the issue, with other Ukrainian officials claiming a full-scale war could began “at any minute.”

Ukraine has claimed a Russian buildup on the other side of the border, though this appears only related to the already announced Russian Navy war games in the Black Sea, and has only involved some additional military helicopters and drones flying along the border region.

Russian President Vladimir Putin did, however, announce that additional security measures would be put in place around critical infrastructure in the Crimean Peninsula, amid fear of sabotage, and said more measures would be taken to prevent future infiltration.

Despite Ukraine’s denials that this most recent event took place, and claims that it’s entirely a Russian invention, sabotage is a serious concern in the peninsula. Twice over the past year, pylons within Ukraine’s Kershon region have been sabotaged cutting off power supplies into the peninsula, with Ukrainian nationalists engaged in efforts to prevent the repairs.