Both nations have boosted production since they were exempted from an OPEC-led deal to cut output, weighing on global prices. This has prompted more talk among producers about including them in the pact.
"We have spoken to (OPEC Secretary General Mohammad) Barkindo and in the next two weeks there will be conversations with them (Libya and Nigeria) and possibly we will invite them to the technical summit," Russian Energy Minister Alexander Novak told reporters on the sidelines of an industry conference in Istanbul.
Six ministers from OPEC and non-OPEC nations including Kuwait, Venezuela, Algeria, Saudi Arabia, Russia and Oman will meet on July 24 in St. Petersburg, Russia, to discuss the current situation in the oil market.
This group, called the Joint Ministerial Monitoring Committee, could recommend expanding the pact to the wider group, which holds its next meeting in November.
The ministerial talks will be preceded by a meeting of a technical committee involving all OPEC and non-OPEC members currently participating in the oil output-cutting deal.
Both Nigeria and Libya were given exemptions to the supply cut, under which OPEC, Russia and other non-OPEC producers are reducing their output by about 1.8 MMbpd because their output has been curbed by conflict.
OPEC delegates have said bringing Nigeria or Libya into the production pact would likely focus on capping their output, rather than asking them to cut their supply so soon after it had recovered from involuntary curbs.
Nigeria's oil minister Emmanuel Ibe Kachikwu has said that Nigeria was not opposed in principle to joining OPEC's production cap, but would have to wait and see if production returned to acceptable levels.
The minister is not planning to attend the Russian talks because he already has another ministerial-level meeting scheduled at home in Abuja, a source familiar with his schedule said.
OPEC has not been in touch with Libya on the issue of capping the country's output, an OPEC delegate said. The Libyan government has not received an invitation to attend the ministerial meeting in Russia, he added.
In comments to Reuters on Monday, the head of Libya's National Oil Corporation did not indicate any willingness to cap output yet, saying Libya's humanitarian problems must be considered in any talks on the subject.
NOC Chairman Mustafa Sanalla added Libya could assist with efforts to stabilize the market by informing OPEC about its plans to restore production.