The leader of the far-right Ukrainian nationalist Pravy Sektor (Right Sector) party has reportedly threatened to attack Russia's lucrative gas pipeline which travels through Ukraine to prevent the Kremlin from sparking a "Third World War".
"We cannot allow the enemy to carry out a blitzkrieg attack on Ukrainian territory," said Dmitry Yarosh, according to Voice of Russia.
The pipeline in question, the Trans-Siberian Pipeline, supplies Europe with the majority of its gas imports.
"We are well aware of the fact that Russia is earning money by transporting its oil and gas to the West through our pipe," he said. "Therefore, we'll destroy this pipe in order to deprive Russia of its financing source."
Yarosh then turned his attention to the situation in Crimea, saying that Russia's takeover would not end in the Russian-majority region and Right Sector would not allow Russia to spark a "Third World War".
"Let the ground burn under the feet of the occupiers! Let them choke on their own blood when they attack our territory! Not one step back! We will not allow Moscow's beserk, totalitarian regime to spark a Third World War!"
The leader of Right Sector issued the threats in an "address to the Ukrainian government and his compatriots".
Yarosh also recently announced that he is to run for the Ukrainian presidency in elections planned for 25 May.
The news was confirmed by the ultra-nationalist movement's chairman Andriy Tarasenko, who said: "Dmytro Yarosh will run for president.
"We are preparing for a congress, at which the party will be renamed, and we will participate in the elections in Kyiv, the elections in all local councils, towns and villages.
"We remain the leaders of this revolution. We are mobilising, we are preparing to react to foreign aggression."
Yarosh, who considers the far-right Svoboda "too liberal", has been issued an arrest warrant by a Moscow court in absentia.
Russia has also been condemned by the US State Department for "inflaming conditions on the streets".