Ukrainian Prime Minister Arseniy Yatsenyuk said Russian troops have entered Ukraine and are working with separatists east of Donetsk. (Reuters)

Ukraine's Foreign Ministry tweeted on Wednesday evening a pair of hashtag slogans, #UkraineUnderAttack and #RussiaInvadedUkraine, urging others to share the message.

Authorities in Kiev claimed Wednesday that Russia was massing troops in Crimea, the Black Sea peninsula that Moscow controversially annexed earlier this year, and pointed to evidence that Russian tanks and helicopters had crossed into Ukrainian territory in a bid to open a "second front" by the coastal city of Novoazovsk. On Tuesday, Ukrainian forces apprehended 10 Russian paratroopers in the eastern Donetsk region. Russian officials said the paratroopers' presence on foreign soil was "an accident."

The Ukrainian Foreign Ministry's tweet is just the latest salvo in a long-running social media war that has shadowed months of geopolitical tensions in the region. In the past week, European and American diplomats have used the hashtag #Escalation as a frame for what they consider to be Russia's hostile actions.

In April, at an earlier stage of the crisis, the Russian Foreign Ministry's English-language account hijacked the #UnitedforUkraine hashtag first promoted by the U.S. State Department. On Wednesday, the same account refrained from deploying any new hashtags but spent most of the day retweeting stinging criticism of NATO by the Russian delegation in Brussels.