The rebel leader Mahmud Jibril was, meanwhile, set to meet with key US lawmakers today to discuss the raging conflict which has left thousands dead and sent more than 750,000 people fleeing the north African country.
Explosions could be heard in eastern Tripoli for almost an hour this morning as jets flew overhead, a witness told AFP.
The explosions began about 7:30 am (0530 GMT) and continued sporadically until 8:15 am (0615 GMT), the witness added.
NATO said that since the alliance took over military operations on March 31 to protect civilians from pro-Gaddafi forces, jets have conducted almost 6,000 sorties, including more than 2,300 strike missions.
Bombs were not dropped during all of those missions, figures showed, as officials insisted again the raids were not aimed at killing Gaddafi, who has ruled Libya for more than four decades.
"All NATO targets are military targets, which means that the targets we've been hitting, and it happened also last night in Tripoli, are command and control bunkers," Brigadier General Claudio Gabellini told reporters yesterday.
"NATO is not targeting individuals," he said via videolink from the operation's headquarters in Naples, Italy.
But asked whether Gaddafi was still alive, the Italian NATO general said: "We don't have any evidence. We don't know what Gaddafi is doing right now." Jets had screamed in low over the capital, Tripoli, in a heavy bombardment lasting roughly three hours on Tuesday morning, an AFP correspondent said.
The blasts came after NATO chief Anders Fogh Rasmussen said time was running out for Gaddafi, who had to "realise sooner rather than later that there's no future for him or his regime." Gaddafi survived a similar NATO bombing on May 1 in Tripoli, which killed his second-youngest son, Seif al-Arab, and three of his grandchildren.