Prime Minister Arseniy Yatsenyuk's promise during an unannounced visit to the blue-collar coal mining region of Donetsk came as militants armed with Kalashnikovs barricaded themselves inside the local administration building and demanded a referendum on joining Russia.
A similar occupation of the state security office of the hardscrabble eastern city of Lugansk has confronted the untested leaders with their biggest challenge since their February ouster of a Kremlin-backed president and decision to strike an alliance with the West.
The decision could limit the supplies of at least 18 European nations for the third time since 2006. Each of the previous interruptions also coincided with attempts by Kiev to pull itself out of the Kremlin's historic sphere of influence.
Putin's warning came after Russia had already hiked Ukraine's energy price by 81 per cent and demanded that his neighbour rewrite its constitution in order to give eastern regions the right to set their own economic and diplomatic relations with Moscow.
Putin's gas threat prompted the US State Department yesterday to denounce "Russia's efforts to use energy as a tool of coercion" and President Barack Obama to raise the possibility of a third and most painful yet round of sanctions against Moscow.
The sabre rattling has set an ominous tone to the first round of international negotiations on Europe's worst crisis in decades that US and EU diplomats had managed to convince both Moscow and Kiev to join in Geneva on April 17.