Russian gas deliveries to Hungary via Ukraine fell by more than 25 percent on Sunday and big gas consumers have been ordered to switch to oil where possible, Hungary's natural gas wholesaler MOL said. The Russian state monopoly, Gazprom, said earlier on Sunday it had cut piped supplies to Ukraine by a quarter -- the level of Ukraine's own imports -- after Kiev refused to sign a new contract requiring it to pay four times as much. Ukraine serves also as a transit country for Russian gas exports to Europe, including Hungary. "Gas shipments are now down by more than 25 percent after a 5 to 10 percent fall in the morning so starting tomorrow, we're ordering big consumers (who have the technology) to switch to oil," MOL spokesman Sandor Kantor told Reuters. Economy Minister Janos Koka said Gazprom told Hungary it continues to pump all of the contracted amount into the pipeline but the gas did not reach the Hungarian-Ukrainian border. Koka added that if deliveries fall by more than 40 percent or if the relatively mild winter weather turns colder, further restrictions are likely. "This is not a Hungarian problem. This is a European Union problem and the EU will have to be the vehicle for finding the solution," Koka told Reuters. "We want Hungary to take a leading role in this."