Ukraine’s President, Viktor Yushchenko, has called for an investigation into a natural gas trading company he views as a tentacle of Russia’s Gazprom, describing its refusal to supply industrial consumers as a “threat to national security.”

While refraining from directly pointing the blame at the Kremlin, Mr Yushchenko on Friday expressed his concern and appealed to the country’s anti-monopoly committee to investigate the actions of Ukrgaz-Energo, a company considered loyal to Russia’s state-controlled Gazprom...