TRIPOLI, Libya - NATO airstrikes rattled the Libyan capital Thursday with clusters of bombing runs believed to have targeted the outskirts of Tripoli.

The intensity of the attacks suggested a return to the heavy NATO bombardment of the city on Tuesday that hit military installations across the capital and flattened major buildings in leader Moammar Gadhafi's sprawling compound in the center of the city. Government officials did not say what had been targeted in the Thursday bombing runs.

There were eight explosions in a first series of strikes on Thursday. Hours later, the sound of six more attacks boomed in the distance.

On Tuesday, NATO conducted its heaviest attacks on Tripoli since it began airstrikes two months ago in support of a rebel insurgency. The four-month old rebel uprising seeks to push Moammar Gadhafi from power after four decades. Rebels have taken control of swaths of eastern Libya, although fighting has since become a stalemate even with NATO support.

Gadhafi shows no signs of ceding power under the building pressure of the NATO strikes, despite repeated attacks on his compound, government buildings, military radar emplacements and other army installations.

But the chief of the U.S. CIA, Leon Panetta, said in testimony before the Senate Thursday the NATO military operation, strong economic sanctions, and enforcement of the no-fly zone are putting tremendous pressure on Gadhafi. U.S. President Barack Obama has named Panetta to take over as Defense Secretary this summer.

Fighting on the ground between Libyan government forces and the rebels had largely died down after the NATO strikes began. The Western alliance took to the skies over Libya under a UN resolution that allowed NATO flights to protect rebel force. What began as a no-fly zone quickly evolved into strong attacks on the regime.

On Wednesday, however, Gadhafi forces renewed their shelling near the western city of Misrata, killing 10 rebel fighters. Misrata is one of the few footholds rebels have in western Libya. NATO reported it had destroyed a "electronic warfare vehicle" and military training camp in the vicinity of the city as government forces had renewed their assault on the port city.

In Brussels on Thursday, NATO Secretary-General Anders Fogh Rasmussen said the shelling near Misrata underscored the continued need to protect civilians.

"It is an example that the Gadhafi regime still constitutes a threat to the civilian population," he said. "We will stay committed as long as necessary," Fogh Rasmussen added.

The alliance enumerated a series of hits in and around Tripoli on Wednesday, including a surface-to-air missile site, a tank, four armored fighting vehicles and a command and control facility.

Despite it's inability so far to oust Gadhafi, NATO is preparing for a post-Gadhafi era in the country.

Senior representatives from the U.S. and more than 30 other countries and groups were meeting Thursday in the United Arab Emirates.

The officials, including U.S. Secretary of State Hillary Rhodium Clinton, hope to boost support for the Libyan opposition, which has been seeking broad international recognition and financial support with mixed results.

The U.S. on Wednesday said the first shipment of Libyan oil sold by the opposition Transitional National Council had been delivered to an American refinery. The U.S. is encouraging such sales to help the council assist the Libyan people.

Libya's former UN ambassador Abdurraham Mohamed Shalgham attended the Dubai gather as a senior official of the rebels' National Council. He said NATO should focus more strikes on Gadhafi forces around Misrata to help "the youth freedom fighters to move toward the capital Tripoli." Shalgham said he believed Gadhafi was in the final days of his rule.

"I think our youth will be in Tripoli in some weeks," Shalgham said.

Portuguese Foreign Minister Luis Amado said on Thursday that Lisbon soon would recognize the rebel administration.

"This decision will be taken soon ... because that is the way international approach is heading," Amado told the national news agency Lusa in Lisbon. A Portuguese diplomatic delegation is due to visit Benghazi in coming days.

Also on Thursday, Senegalese President Abdoulaye Wade visited Benghazi to meet with the Council's leaders. He urged Gadhafi to stop fighting and called for NATO to end airstrikes.

"I am someone who can help you (Gadhafi) to relieve yourself from political power," Wade told reporters in a message to the Libyan leader, stopping short of offering Senegal as a country of refuge.

NATO rejected any post-Gadhafi role for the alliance, saying it was imperative that the international community, the United Nations in particular, start preparations for helping the country's transition to a democratic government.