Ukrainian residents are reporting that their nation’s military is massing troops and heavy military equipment along the border with the Crimean Peninsula today, following reports from Russian officials of an attempted infiltration of the peninsula, which the Russians identified as a Ukrainian government incursion, and attempted terrorist plot. A Russian soldier and a member of the FSB security service were reported slain in that weekend incident.

Details of the weekend incident are still emerging, but Russian officials reported gunfire, and having captured several of the plotters, who they suspect of being with Ukrainian intelligence, who were aiming to set up a spy network to attack infrastructure in the peninsula.

Ukrainian military spokesman Andriy Lysenko confirmed the buildup, amid claims of Russian helicopters spotted inside Crimean territory. He added that Ukrainians “should understand that at any minute” a large-scale war with Russia could begin.

Ukrainian officials went on to claim Russian President Vladimir Putin was plotting to invade them because of the weekend cross-border incident, though of course Ukraine’s government has been predicting an imminent Russian invasion for over two years now, with nothing coming of it.

Those predictions of war rarely come with the overt military buildup, however, and Ukrainian officials clearly have more in mind than just the usual week of hysteria that comes and goes without incident, particularly since it coincides so neatly with the reports of an incident at the exact same border.

Crimea was annexed by the Russian Empire in 1783, and the city of Sevastopol became the host of the Russian Black Sea Fleet the same year. The peninsula’s status was shifted twice within the Soviet Union, initially being an independent Soviet Socialist Republic, becoming part of the Russian SSR in 1945, and transferred to Ukraine SSR in 1954. Ukraine retained Crimea as an autonomous region when the Soviet Union split, though Russia retained the base at Sevastopol and it was agreed the city would have a “special status.”

This arrangement fell apart in 2014, with the revolution in Ukraine which ousted a pro-Russian government. Crimea quickly seceded from Ukraine and was granted accession into the Russian Federation. Ukraine does not recognize this transfer, and continues to present Crimea as being under “military occupation.”

The Crimean Peninsula has suffered significant sabotage attacks since its reversion to Russian control, with its electricity supply twice interrupted by saboteur attacks, and Ukrainian nationalists preventing the repairs. Russia aims to supply all of Crimea’s power needs directly, via undersea cable, by 2020, and also plans a land connection, by bridge, in 2018.