Libya's government warned that it would sue any international company that concluded energy deals with rebels who control some of the country's oil infrastructure, the state news agency reported.
The threat is likely to make it more complicated for the rebels based in eastern Libya to sell oil on the international market, a trade they had been counting on to finance their insurgency against the rule of Muammar Gaddafi.
"The National Oil Corporation is the entity authorised by law to deal with external parties. Because of the strategic importance of these goods oil and gas at the global level, no country can leave their management to armed gangs," said a government communique carried by the Jana news agency.
"The Libyan state will sue any party that seals deals regarding Libyan oil with parties other than the National Oil Corporation," it said.
A senior Libyan rebel official said on Sunday a Gulf oil producer, Qatar, had agreed to market oil produced from east Libyan fields that are no longer under Gaddafi's control.
On Monday, Qatar became the first Arab country to recognise the rebels. A U.S. official said crude oil sales by Libyan rebels would not be subject to U.S. sanctions if they were not connected to Gaddafi's government entities.
However, energy trading sources say shipping and legal risks mean it is unlikely the rebels will be able to market their oil abroad for several weeks.
