MOSCOW - Russian President Dmitry Medvedev said he hoped Ukraine would stick to its existing gas agreement with Russia despite tension between the two on the issue, according to media reports.

"So far, there's no conflict," Medvedev told Euronews in an interview broadcast early Friday. "Rather there are differences that may lead to various developments."

The Russian president called Ukraine one of Russia's close partners and friends, but said Ukraine "must learn that you can't torpedo existing contracts - even if you don't like them".

"It is completely unacceptable. All agreements, as long as they are not refuted in court or abandoned by the parties, must be carried out," Medvedev said.

"I hope our partners, our Ukrainian friends will likewise stick strictly to the framework agreement concluded in 2009," he said.

Meanwhile, Medvedev reiterated that Russia was "willing to discuss various cooperation schemes" with Ukraine, including "advanced plans" based on Ukraine's integration into the Customs Union.

The Ukrainian government has long urged Russia to review the existing gas pricing formula, but the two sides have not yet reached consensus on the issue.

Medvedev said last week Ukraine might get discounts for gas if it joined the Customs Union, which groups Russia, Belarus and Kazakhstan. But Ukrainian Prime Minister Mykola Azarov said Kiev wanted no discount but a fair contract.