TRIPOLI: NATO aircraft destroyed the guard towers at Muammar Gaddafi's compound in Tripoli, a NATO official said Saturday, then staged a rare daytime airstrike on the Libyan capital, heightening pressure on him to quit. “RAF Typhoons, along with other NATO aircraft, last night used precision-guided weapons to bring down guard towers along the walls of Col. Gaddafi's Bab Al-Aziziyah complex in the center of Tripoli,” Major General John Lorimer, chief British military spokesman, said in a statement. “Last night's action sends a powerful message to the regime's leadership and to those involved in delivering Col. Gaddafi's attacks on civilians that they are no longer hidden away from the Libyan people behind high walls,” he said. “The massive compound has not just been his home, but is also a major military barracks and headquarters, and lies at the heart of his network of secret police and intelligence agencies,” Lorimer said. “Previous NATO attacks have hit command and control and other military facilities within the complex.” NATO followed its fifth straight night of attacks with a daytime strike that produced smoke coming from the area of the Gaddafi compound. A big boom shook Tripoli at about 0800 GMT but it was unclear if it was caused by a bomb or missile. A NATO military spokesman said the daylight raid targeted “a vehicle storage compound 600 to 800 meters to the east of Gaddafi's so called tent private area. It is not part of the main Gaddafi complex”. Following the Friday night strikes, the Libyan state broadcaster said NATO raids also caused “human and material” damage near Mizda, to the south. NATO said it was preparing to deploy attack helicopters over the Arab North African state for the first time to increase the pressure on Gaddafi's forces on the ground. Rebel-held Misrata, Libya's third biggest city and scene of some of the fiercest battles in the conflict, suffered a second day of heavy fighting on its western outskirts Friday. Gaddafi's forces stepped up their attacks too on Zintan, part of a chain of mountain settlements near Libya's border with Tunisia, where rebels have been holding off assaults for months. The pro-rebel Libyan Youth Movement, in an open Internet letter to United Nations Secretary General Ban Ki-moon, appealed for help for the people of two western towns, Yafran and Al-Qala'a, which it said had been under siege by government forces since April 3.