An apparent NATO airstrike again targeted the area near Moammar Gadhafi's compound during a pre-dawn raid in the Libyan capital Tripoli.
At least two thunderous booms were heard in quick succession shortly before 5 a.m. Thursday in the capital. A column of smoke could be seen rising from the vicinity of the Libyan leader's Bab al-Aziziya compound.
It was not clear what was hit. Government officials did not immediately comment on the strike.
NATO warplanes have repeatedly targeted the area in and around the compound, which sits in the heart of Tripoli.
Earlier Wednesday, Libyan rebels pushed deeper into government-held territory south of the capital, but their advance came as strains began to emerge in the Western alliance trying to topple Moammar Gadhafi.
In Washington, a bipartisan group of lawmakers is suing President Barack Obama for taking military action against Libya without war authorization from Congress.
Fighters in the Western Mountains, a rebel stronghold about 90 miles southwest of Tripoli, built on gains made in the past few days by taking two villages from which pro-Gadhafi forces had for months been shelling rebel-held towns.
But the rebels are still a long way from Gadhafi's main stronghold in Tripoli, while their fellow fighters on the other two fronts — in Misrata and in eastern Libya — have made only halting progress against better-armed government troops.
"The revolutionaries (rebels) now control Zawiyat al-Babour and al-Awiniyah after pro-Gadhafi forces retreated this morning from the two villages," Abdulrahman, a rebel spokesman in the nearby town of Zintan, told Reuters.
Libyan state TV said on Wednesday a NATO bombardment had killed 12 people in a convoy in the town of Kikla, 90 miles southwest of Tripoli. A NATO official denied the report, saying: "There was no strike in Kikla by NATO today."
The rebels seized the town on Tuesday after government troops fell back.
Ties are becoming strained in the NATO alliance, with some NATO members complaining that others have been reluctant to commit additional resources needed to sustain the bombing mission in the coming months.
Adding to the pressure, lawmakers in the Congress are pressing Obama to explain the legal grounds on which he was keeping U.S. forces involved in Libya without the authorization of Congress.
In response, the White House sent lawmakers a detailed report Wednesday outlining the objectives of U.S. military involvement in Libya and making a legal case for continuing the campaign. The Obama administration said U.S. military action in Libya does not require congressional authorization because American forces are now playing a support role.
Senior administration officials said the White House believes that because U.S. forces are not engaged in sustained fighting and there are no troops on the ground in Libya, the president has the authority to direct the mission.
Cameron: 'Time is on our side'
Speaking in London after meeting NATO Secretary General Anders Fogh Rasmussen, British Prime Minister David Cameron reiterated that time was running out for Gadhafi and that the alliance was as determined as ever.
"I think there is a very clear pattern emerging which is time is on our side, because we have the support of NATO, the United Nations, the Arab League, a huge number of countries in our coalition and in our contact group," he said.
Rasmussen echoed those comments despite senior NATO commander General Stephane Abrial on Tuesday raising questions about the alliance's ability to handle a long-term intervention.
As NATO reportedly resumed its airstrikes on Tripoli late Tuesday, a London newspaper said Gadhafi's son, who heads the country's Olympic committee, received nearly 1,000 tickets to London's 2012 Olympic Games.
Responding to the report in Britain's Daily Telegraph, a spokeswoman for London 2012 said Libya has been given hundreds of tickets to the events, but noted the tickets went to Libya's Olympic Committee — "not an individual" — for distribution to sports organizations and athletes.
The London Olympic organizing committee is obliged to give tickets to any of the International Olympic Committee member states who request them.
But key members of Gadhafi's regime are under travel bans and there is no indication the Libyan leader or his son plan to — or could — attend the Olympics.
According to the Daily Telegraph report, organizers have privately expressed fears that Gadhafi could crash the games using the allocated tickets. But a U.K. government spokesman told the newspaper that Gadhafi wouldn't be allowed to attend because of both an international travel ban placed on him and the International Criminal Court's warrant for his arrest.
The Daily Telegraph also reported people inside the U.K. government sought out guidance on how to prevent dictators, , from attending the games in an effort to avoid diplomatic spats. The newspaper reported that authorities offered reassurance by noting that travel bans placed on such figures would render the issue moot.
East of Tripoli, alliance aircraft have begun dropping leaflets warning government troops to abandon their posts outside Zlitan, which lies just west of the rebel-held port city of Misrata.
Rebel forces have been advancing along the Mediterranean coast toward Zlitan, but say they have been instructed by NATO to withdraw ahead of expected bombing runs to old front lines in Dafniya.
The 3-by-5 inch leaflets intended for forces loyal to Gadhafi carry the NATO symbol and a picture of an Apache attack helicopter and burning tanks on one side. Green Arabic writing warns: "There's no place to hide. It's not too late to stop fighting. If you continue to threaten civilians, you will face destruction." The message on the reverse urges soldiers to "stop and stay away from fighting now."
An Associated Press reporter near the front line said NATO fighter jets could be heard overhead.
Battle for Zlitan
If the rebels take Zlitan, they would be within 85 miles of the eastern outskirts of Tripoli. A rebel official said opposition leaders in Zlitan have been meeting with their counterparts in Misrata, but he acknowledged they face challenges in advancing on the city.
"We need the people of Zlitan to push more courageously forward. They are dependent on our movements, but the problem is only a third of that city is with the rebels," said Ibrahim Beatelmal, a rebel military spokesman in Misrata.
NATO's nearly three-month air campaign has grounded Gadhafi's air forces and weakened his military capabilities. But there are more signs the pace of operations has put a strain on the trans-Atlantic alliance.
In London, the head of the Royal Navy warned that the British fleet — a key contributor to the Libya mission — will be unable to maintain the pace of operations if the mission drags on until the end of the year.
Adm. Mark Stanhope told reporters Monday he was comfortable with NATO's decision to extend the Libya operation to the end of September, but said that beyond that the government would need to make "challenging decisions."
"If we do it longer than six months we will have to reprioritize forces," he said.
Elsewhere, a senior NATO official said coalition resources would become "critical" if intervention in Libya continues.
"If additional resources are needed, this of course will need a political decision," said the official, Gen. Stephane Abrial, Supreme Allied Commander Transformation.