A match appeared to have been struck to the smouldering tinder of the conflict in Ukraine this week, with both Russia and NATO accusing the other of interference in the country.
Russia's Foreign Ministry warned of the possibility of "civil war" if "military preparations" by Ukraine did not stop.
Late Tuesday, the Ukrainian security service issued a statement saying a group of separatists had placed explosives in a seized building in the eastern city of Luhansk and were holding about 60 people against their will.
Earlier Tuesday, around 70 people were arrested in eastern city Kharkiv after protesters in favor of a Crimea-style annexation by Russia stormed government buildings. This followed the escalation of pro-Russian protests, which some in Ukraine allege are backed by the Russian government, in recent days.
These actions add to fears that the Russian government may intervene directly in its struggling neighbor, which would lead to further economically-damaging sanctions from the Western governments.
"If Russia were to intervene further in Ukraine it would be a historic mistake," NATO secretary-general Anders Fogh Rasmussen told a news conference in Paris.
"It would have grave consequences for our relationship with Russia and would further isolate Russia internationally."
Russia countered with accusations that U.S. mercenaries had been operating in Ukraine, while wearing the uniforms of Ukraine's Sokol, its special forces.
"The biggest concern on the ground is, if we start seeing fatalities, particularly of Russian protestors, does that give Putin an excuse to lead a further invasion?" Raoul Ruparel, head of economic research at Open Europe, told CNBC.