KIEV — The Ukrainian interior ministry said on Sunday its forces had taken full control of the country's gas transport and distribution system and put it under special guard.

In a statement, it said the order from the prime minister had been given "to ensure the security and smooth operation of the country's most important infrastructure asset".

It gave no further detail or explanation. Ukraine is in turmoil following last month's overthrow of the Moscow-backed president and the Russian takeover of the Crimea peninsula.

With the Kremlin warning that it might send forces to protect Russian speakers from Ukrainian nationalists, Ukrainian media have quoted one prominent far-right group saying it could punish a Russian invasion by attacking pipelines that carry Russia's gas exports through Ukraine to Western Europe.