A deadly terrorist attack on a peaceful pro-Ukrainian demonstration in the country’s eastern city of Kharkiv threatens to send an already tense conflict between the two Eastern European powers spiraling further out of control.

Three people were killed, including a 15-year-old boy, when a bomb tore through a crowd in the city located 140 miles away from the border oblasts that Russia is actively destabilizing and reinforcing with troops and equipment. The demonstration was one of many held across the country in honor of the memory of those who died in the protests that resulted in the collapse of Viktor Yanukovych’s government one year ago.

In a dangerous development, Ukrainian officials are accusing Moscow of providing the bombers who executed this attack with training and equipment (via Newsweek):

Markian Lubkivskyi, an aide to the head of Ukraine’s SBU security service, said four suspects had been arrested. They were planning to conduct a series of attacks in the city with a Russian-made “Shmel” rocket launcher, he said.

“They are Ukrainian citizens, who underwent instruction and received weapons in the Russian Federation, in Belgorod,” he told Ukraine’s 112 Television. Belgorod is a city across the nearby Russian border from Kharkiv.

Olexander Turchinov, secretary of Ukraine’s National Security and Defence Council, said Kharkiv was put under high alert in an anti-terrorist operation.

Moscow did not immediately respond to the accusations. It has long denied aiding its militant sympathizers in Ukraine.

In another disturbing development that could inflame tensions in Europe, the Russian media outlet Novaya Gazeta indicated in a report over the weekend that documents it had obtained suggest that the Russian Federation planned to invade Ukraine prior to Yanukovych’s fall. What’s more, that plan included dividing Ukraine into distinct districts with a plan to reintegrate the eastern portion of the country back into the Russia tax sphere and eventually to annex portions of the country into the Russian Federation.

[Gazeta editor Dimitri] Muratov said the document characterized then Ukrainian President Viktor Yanukovych as “a person without morals and willpower whose downfall must be expected at any moment.” Yanukovych fled Ukraine for Russia on Feb. 22, 2014.

Muratov said the Russian document appears to have been drafted between Feb. 4 and Feb. 15 last year. He said the overall strategy included plans on how to break Ukraine into autonomous sectors, immediately attaching now war-torn southeastern Ukraine to Moscow’s tax union, with a longer term plan for annexation.

The plan suggested “the main thrust should be Crimea and the kharkiv region, with the aim of initiating the annexation of the eastern regions.”

The strategy document also calls for a public relations campaign to justify Russia’s intervention. The newspaper did not release further details of the strategy at this point.

Performing independent journalism in Russia is a particularly dangerous practice, and publicly disclosing Russian defense documents related to the covert operation in Ukraine will certainly require a response. Gazeta ‘s journalists are today wearing targets on their backs.

Though this document undermines Moscow’s claim to have invaded and annexed the Crimean peninsula in response to an acute crisis and public unrest following the dissolution of the last Ukrainian government, there will be some cynical circles in the West in which this bombshell is met with a yawn. Nothing would so aid Vladimir Putin in the pursuit of his ambitions in Ukraine than Western indifference. Egregious violations of sovereignty, including allegations that Russia helped execute a terrorist attack on a peaceful demonstration and plotted the dismemberment and reintegration of a neighboring nation without pretext, must be forcefully opposed lest they repeat.