Tripoli, Libya (CNN) -- Several explosions rattled Tripoli Thursday morning as Libyan state television reported bombardments in Sirte, east of Tripoli, and other areas.
A Russian envoy due to arrive in Libya Thursday raised the possibility of leader Moammar Gadhafi giving up power but remaining in the country.
"There is a possible option where Gadhafi continues living in Libya as a private individualwith his people and his tribe but relinquishes power and his family stays away from taking economic decisions," Mikhail Margelov said, according to the country's Itar-Tass news agency.
Margelov said last week that the rebel Transitional National Council did not need "Gadhafi's head, and no one is going to scalp him and nail it to the wall in his office," the agency reported.
Margelov is due to meet top Libyan officials, he said before leaving Moscow, but it is not clear that Gadhafi will be among them.
He has already talked to the opposition in Benghazi, the de facto rebel capital, and consulted with Ahmed Gaddafi al-Dam, a cousin of Gadhafi's, in Cairo, he said.
His mission to Tripoli comes as critics have questioned NATO's involvement in the civil war.
U.S. lawmakers filed a suit Wednesday that challenges the nation's participation in the Libya mission.
The lawmakers have accused President Barack Obama of failing to consult with Congress over the military effort in the North African country.
The White House denied that accusation, saying Obama has not violated the War Powers Resolution by intervening militarily for more than 60 days without seeking approval from Congress.
South African President Jacob Zuma on Tuesday slammed the international coalition's operation in the battle.
NATO started airstrikes in Libya in March to enforce a U.N. resolution to protect civilians from forces loyal to ruler Moammar Gadhafi.
But Zuma said actions by the international coalition have exceeded the authority that the resolution granted.
"We strongly believe that the resolution is being abused for regime change, political assassinations and foreign military occupation," Zuma said at a budget vote debate before the National Assembly in Cape Town on Tuesday.
Meanwhile, rebel forces said they have made progress in recent days in the fight against Ghadafi forces.
Rebels have taken control of the mountainous Jebel Nafusa region, which is southwest of Tripoli, said Ahmed Bani, an officer with the rebel forces.
Rebels have also made gains in the western city of Zlitan, Bani said.CNN's David McKenzie and Ben Wedeman contributed to this report.
