Russia and Ukraine have postponed the signing of a controversial gas agreement until next week because they say some of the details have yet to be finalised.

The five-year deal was reached this month after Russia suspended gas supplies to Ukraine on New Year's Day, leaving several other European countries without a supply.

The deal will double the price Kiev pays for gas to $95 per 1,000 cubic metres.

Questions have been raised in Ukraine over whether the country's government had the authority to sign the agreement.