LONDON -- Oil prices rose on Thursday as OPEC said it was not yet clear whether the exporters' cartel would relax tough supply curbs next month.

Traders expect the Organization of the Petroleum Exporting Countries to lift output in the fourth quarter when demand normally peaks for the northern hemisphere's winter, AFP reported.

"we cannot make a firm prediction of the market situation, especially at this time," OPEC Secretary General Alvaro Silva was quoted as saying on OPEC's official news agency.

Cartel insiders said recently that OPEC is likely to raise production to meet rising extra winter demand and feed economic growth, Reuters reported.

International benchmark Brent crude oil rose 15 cents to $25.15 a barrel by late afternoon in London, while U.S. crude futures climbed 17 cents to $26.67.

OPEC officials have previously said that an output hike of about a million barrels per day was one option open to the group of mostly Middle Eastern countries that control two-thirds of world exports.

But some economists now believe that the recent slide in global stock market could hit growth and oil demand later this year.

The 10 OPEC members with output quotas, excluding sanctions-bound Iraq, have an agreed ceiling of 21.7 million barrels daily. They are estimated to be leaking at least 1.5 million bpd above those official limits.