"The Libyan premier told me: if the rebels seize the city, we will cover it with missiles and blow it up," Kremlin envoy Mikhail Margelov said in an interview with the the Izvestia daily.
Margelov met Libyan Prime Minister Baghdadi al-Mahmudi last month.
"I imagine that the Kadhafi regime does have such a suicidal plan," he added, saying that Kadhafi still had plentiful supplies of missiles and ammunition.
But Margelov, who has had rare access to senior Libyan officials, questioned reports that Kadhafi could be running out of arms in the drawn-out conflict.
Kadhafi had still not used a single surface-to-surface missile, he argued.
"Tripoli theoretically could lack ammunition for tanks, cartridges for rifles. But the colonel has got plenty of missiles and explosives."
Margelov met the Libyan prime minister on June 16 in Tripoli after holding talks in Benghazi earlier the same month. He has not met Kadhafi himself.
Russia abstained from a vote on a March UN Security Council resolution that opened the way for foreign involvement and has since criticized the campaign - particularly arms drops by France.
Russian Foreign Minister Sergei Lavrov met US Secretary of State Hillary Clinton on Wednesday for talks on Libya, where Lavrov sought to play down differences between the countries.
However, the Russian foreign ministry said earlier Wednesday that Moscow would not take part in talks on Libya later this week in Turkey, which has also seen itself as a mediator in the conflict.