Tripoli , Libya ( CNN ) -- As Moammar Gadhafi 's inner circle showed possible signs of cracking Friday , heavily armed forces loyal to the Libyan leader continued pounding cities that were once some of the country 's most prosperous places . Officials and analysts said the surge in firepower from the Libyan government sends a message : Gadhafi is determined to prevail , and defections of some of his high-profile allies are making him nervous . `` You 're certainly getting evidence that there are a lot of tensions . ... Each person that leaves , that makes it a little scarier for the people that are still remaining . And you may , at some point , get a tipping effect , '' said Anne-Marie Slaughter , a professor of international affairs at Princeton University . On Thursday word emerged that Gadhafi 's pick for U.N. ambassador had defected to Egypt -- a day after Libya 's foreign minister fled to London and told the government there that he had resigned . Citing unnamed British government sources , the Guardian newspaper reported Friday that a senior adviser to one of Gadhafi 's sons was in London for secret talks with British officials . The adviser to Saif al-Islam Gadhafi , Mohammed Ismael , told CNN earlier this week that he would be traveling to London for family reasons . Calls placed to his mobile phone by CNN on Friday were not answered . Asked about the Guardian report , a UK Foreign Office spokesman neither confirmed nor denied it . `` We are not going to provide running commentary on our contacts with Libyan officials , '' the spokesman said . `` In any contact that we do have , we make it clear that Gadhafi has to go . '' Rebel fighters also said they remained determined to topple Gadhafi 's nearly 42-year reign . But the battles over key cities are far from over . Rebels massed on the outskirts of the government-controlled oil town of al-Brega , which has changed hands six times in six weeks under dramatically shifting circumstances in the country 's civil war . Misrata , Libya 's third largest city and the final rebel stronghold in the western part of the country , was under siege by pro-Gadhafi forces . Badly damaged buildings lined streets covered with wreckage after weeks of urban combat . Witnesses said most residents fled the downtown area after government forces positioned snipers on tall buildings and used tanks and artillery in the city center . Clearly outgunned , opposition forces have pinned their hopes on more NATO airpower . `` We want to bring a speedy end to this , '' Col. Ahmed Omar Bani , an opposition spokesman , told CNN . `` A strike is not a strike unless it kills . '' U.S. officials claim Gadhafi 's military capabilities have been steadily eroded since the onset of U.N.-sanctioned airstrikes . But the dictator 's forces still outnumber rebels by about 10-to-1 in terms of armor and other ground forces , Joint Chiefs of Staff Chairman Adm. Mike Mullen told the House Armed Services Committee Thursday . U.S. Defense Secretary Robert Gates , also speaking before the House committee , warned that the Libyan rebels still need significant training and assistance . `` It 's pretty much a pickup ballgame '' right now , he said . U.S. and British officials say no decision has been made about whether to arm the opposition . Gates reiterated the Obama administration 's promise that no U.S. ground forces will be used in Libya , telling committee members that the rebels had indicated they did n't want such an intervention . But the United States does have CIA personnel on the ground . CIA operatives have been in Libya working with rebel leaders to try to reverse gains by loyalist forces , a U.S. intelligence source said . The United States , insisting it is now fulfilling more of a support role in the coalition , shifted in that direction as NATO took sole command of air operations in Libya . A U.S. intelligence source said the CIA is operating in the country to help increase U.S. `` military and political understanding '' of the situation . But officials leaving Libya may end up playing a more decisive role than troops or CIA agents on the ground . After defecting Wednesday , former Libyan Foreign Minister Moussa Koussa was voluntarily speaking with officials in the United Kingdom , British Foreign Secretary William Hague said . Hague said Koussa 's departure from Libya provides evidence `` that Gadhafi 's regime ... is fragmented , under pressure and crumbling from within . '' Koussa did not tell the Libyan government he was planning to quit before he arrived in Britain , Libyan government spokesman Moussa Ibrahim said Thursday . But Ibrahim downplayed the defection itself , saying Koussa was an old man in poor health who had not been able to handle the pressure of his job . On Thursday an opposition leader and a relative said that the man Gadhafi tapped as the country 's U.N. envoy had defected to Egypt . Former Foreign Minister Ali Abdussalam Treki , who recently served as the president of the U.N. General Assembly , was to replace Abdurrahman Mohamed Shalgham as ambassador in New York . But he never arrived . Such defections are significant , but not as important as the departure of one of Gadhafi 's family members would be , according to Robert Baer , a former CIA operative in the Middle East . `` Crack that clan and he 's done . Those elite units will fall apart , the tribe will defect , and it will all be over , '' Baer told CNN 's AC360 . CNN 's Frederik Pleitgen , Ben Wedeman and Nic Robertson contributed to this report .
Libya 's foreign ministry says Libya 's former foreign minister is speaking with officials . Report : A senior adviser to one of Hussein 's sons was in London for talks . The battles over key cities are far from over . Libyan military leaders officials say Libyan opposition forces are retreating .