A Russian marine has apprently shot dead a Ukrainian officer, in what Ukrainian authorities insinuated was one of a number of ploys to cause disorder so Russia could further invade the eastern part of the nation.
Ukraine's defence ministry announced the death on Sunday evening, and said it had occurred in the town of Novofyodorovka, on the Black Sea coast.
It is one of the few casualties of the relatively bloodless Crimean conflict, which has seen Russia annexe the Black Sea peninsula after a controversial speedy referendum.
A criminal investigation will now take place, but Ukraine's prime minister Arseniy Yatsenyuk has accused Russia of deliberately sowing seeds of disorder as a pretext for further Russian incursion into eastern Ukraine.
Russian media said that the Ukrainian soldiers had been drinking in the village, and had picked an argument with Russian troops outside their base, resulting in shots being fired.
In a statement, the ministry said the man was shot twice "at close range from an AK-47", once in the chest and the other in the face.
Russian troops are now stationed within 19 miles of the eastern Ukrainian border, and the interior ministry reported Sunday that unidentified armed man, thought to be pro-Russian activists were occupying a security services building in eastern Ukraine's Luhansk, close to the Russian border.
"The plan is to destabilise the situation, the plan is for foreign troops to cross the border and seize the country's territory, which we will not allow," he told a meeting of ministers..
"An anti-Ukrainian plan is being put into operation, under which foreign troops will cross the border and seize the territory of the country. We will not allow this," he said.
Interior Minister Arsen Avakov accused Russian President Vladimir Putin of orchestrating "separatist disorder" in the region as a pretext for an invasion.
Around half of eastern Ukraine's citizens speak Russian and are ethnically Russian. The occupation of the building in Luhansk echoes the occupation of Crimea's parliament building by pro-Russia activists in March, just before Putin gave orders for Russian troops to seal the peninsula, leading to the subsequent referendum and annexation by Russia.
"Unknown people who are in the building have broken into the building's arsenal and have seized weapons," a police statement said, according to Reuters.
Ukraine's Russian minority have voiced fears, echoed by Putin, that they will be repressed and banned from speaking their native tongue under the new Ukrainian regime.
Ukraine's interim government denies this has occurred, or will take place.
On March 18, a Ukrainian soldier was fatally shot a base in Crimea, near the regional capital of Simferopol. A member of a pro-Russian Crimean “self-defence” unit was also killed in the clash.