LONDON—Russia's state-controlled gas company OAO Gazprom said Monday it was considering whether to extend the pricing contract for Ukraine's natural gas imports, heightening concerns over potential disruptions to supplies as the crisis between the countries spilled into energy markets.

In a presentation to investors in London, Gazprom's Chief Financial Officer Andrei Kruglov said Russian gas supplies to Europe via Ukraine were unaffected, but Gazprom had concerns over payments.

"The situation with payments is worrying. Ukraine is paying but not as well as we would like it to... We are still thinking about whether to extend the pricing contract into the next quarter, based on current prices," Mr. Kruglov told investors, according to a spokeswoman for the company.

Ukraine's Minister of Energy and Coal Industry Yury Prodan said the country aimed to repay $400 million for February gas supplies, Interfax reported. The total debt owing for energy to Russia is $1.5 billion.

"We have today the debt that the previous leadership of the country has left us. We continue to pay this debt, but of course, we cannot pay (at) so sharp a pace to repay the entire debt... In the near future, we want to repay current payments that are about $400 million in February," Mr. Prodan said on Monday at a briefing in Kiev, according to Interfax.