MOSCOW, June 3 – Russian President Dmitry Medvedev and Prime Minister Vladimir Putin on Wednesday stepped up pressure on Ukraine, threatening severe penalties if the country fails to pay for natural gas within days.

Naftogaz Ukrayiny must pay about $650 million to Gazprom by June 7 for importing about 2.4 billion cubic meters of natural gas in May, but the Ukrainian company has been facing financial difficulties.

“Ukraine must pay according to the signed agreement whether anybody likes it or not,” Medvedev said in Moscow, quoted by Interfax-Ukraine. “This is not a joke. This is a normal legal practice.”