"We are ready to deliver (oil), we have a contract, but if any of the transit countries abuse, what can you do?" Putin was quoted by Russian news agencies as saying.
"We have a contract to deliver oil. I think that this contract will be fulfilled," he added.
His comments came after Ukraine said Monday it wanted to change the terms of its 2004 transit contract with Russia for oil shipments via Ukrainian territory to the European Union.
Earlier on Tuesday, Russia's Deputy Prime Minister Igor Sechin said Russian oil shipments to Europe through Ukraine will continue without disruption as the two countries renegotiate their transit agreement.
"We expect that there will be no problems with the transit," Sechin was quoted as saying by the RIA Novosti news agency.
Ukraine had sought and obtained an increase in the tariffs Russia pays to transit its oil through Ukrainian pipelines, but the two sides had still not agreed on how much oil -- subject to those tariffs -- Russia would "guarantee" to pump through Ukraine, officials said.
Sechin said Russia was still negotiating with Ukraine on the final terms of the new deal.
Disputes between Russia and Ukraine on pricing and transit of Russian natural gas shipped to EU clients have caused serious supply disruptions in recent years, but Ukrainian officials gave assurances that transit would continue even if talks were not concluded by the end of the year.
EU sources in Brussels also played down fears of another looming energy dispute between Russia and Ukraine that could have an impact on EU energy supplies.