OPEC sought on Wednesday to build momentum for its plan to cap global oil production, saying it will extend invitations to more non-member producers after holding informal talks with Russia and Mexico in Istanbul.

Representatives of OPEC and non-OPEC countries will hold a technical meeting on October 28-29 in Vienna to continue to discuss “a road map” towards an agreement, Qatar’s Energy Minister Mohammed al-Sada told reporters after the meeting on the sidelines of the World Energy Congress in Istanbul.

It was unclear which other countries would join the initiative.

No specific production figures were discussed during Wednesday’s meeting but more details will likely be discussed at the technical meeting in Vienna, Russian Energy Minister Alexander Novak said.

Russian President Vladimir Putin said on Wednesday he saw no obstacles to a global agreement on an oil output freeze.

The Organization of the Petroleum Exporting Countries last month in Algiers agreed on a modest production cap to a range of 32.50-33.0 million barrels per day (bpd). OPEC last month pumped 33.39 million bpd. [OPEC/M]

Al-Sada said there had been a “positive understanding of the situation on what could be the role of OPEC and what could be the role of non-OPEC” in balancing the oil market.

The International Energy Agency said global oil supply could fall in line with demand more quickly if OPEC and Russia agree to a steep enough cut in production, but it is unclear how rapidly this might happen. [IEA/M]

Any deal would face challenges from a 3 billion barrel global inventory build in recent years as well as efforts by OPEC members Libya and Nigeria to increase production curtailed by conflict.

Iran is also seeking to return its production to levels reached before it was hit by international sanctions in 2012.

(Reporting by Rania El Gamal, Ron Bousso and Parisa Hafezi)