Russia has strongly criticised France for dropping weapons to Libyan rebels and demanded an explanation from Paris.
"If this is confirmed, it is a very crude violation of UN Security Council resolution 1970," Foreign Minister Sergei Lavrov said.
The African Union has also criticised the move, saying it risks causing a "Somalia-sation" of Libya.
The French military says it has dropped arms to Berber tribal fighters in the mountains south-west of the capital.
Mr Lavrov said Russia had formally requested information from France about the move, to check that it "corresponds with reality".
Mr Lavrov is due to meet French counterpart Alain Juppe in Moscow on Friday.
Moscow abstained from the UN Security Council vote in March that authorised an international mission in Libya to protect civilians.
Russia and China have both criticised the Nato campaign in recent weeks, saying it had gone beyond the remit of UN resolution 1973.
Another resolution, 1970, had imposed an arms embargo on Libya.
But US and UK officials have argued that resolution 1973 could nonetheless allow weapons to be supplied to rebels fighting to topple Libyan leader Muammar Gaddafi.
France is also said to have been concerned at the stalemate in the Libyan conflict, which began in February.
Libyan rebels have recently been making gains and hope to advance on Tripoli from the existing front line on the northern side of the Nafusa mountains about 65km (40 miles) from the capital.
French officials have said the arms dropped to rebels earlier this month were for the protection of civilians threatened at the time by pro-Gaddafi forces.
"It appeared that in certain zones the security situation was extremely tense for these undefended populations," French military spokesman Thierry Burkhard said on Thursday.
He said the supplies had been limited to ammunition and "light arms" including machine guns and rocket launchers. He denied a report in Le Figaro newspaper that anti-tank missiles had been parachuted in.
French media reports have said "light armoured cars" were also delivered to the rebels from Tunisia, and that France had not informed its allies about the move.
Earlier on Thursday, African Union chief Jean Ping listed a number of "problems" linked to France's decision to air-drop weapons to the rebels.
"The risk of civil war, risk of partition of the country, the risk of 'Somalia-sation' of the country, risk of having arms everywhere... with terrorism.
"These risks will concern the neighbouring countries," said Mr Ping, speaking at an African Union summit in Equatorial Guinea.