UN chief Ban Ki-moon told Libyan leader Moamer Kadhafi on Monday that violence in the country ``must stop immediately'' and called for a broad-based dialogue, a UN spokesman said. Ban had ``extensive'' telephone talks with the beleaguered Libyan leader, UN spokesman Martin Nesirky said. ``The secretary general expressed deep concern at the escalating scale of violence and emphasized that it must stop immediately. ``He reiterated his call for respect for basic freedoms and human rights, including peaceful assembly and information,'' Nesirky said. In another development, Libyan security forces have launched an operation against ``dens of terrorists'' in a sweep that has killed a number of people, state television reported on Monday. The report did not give further details on where the operation was being carried out nor on the identity of those being targeted. Security forces ``stormed the dens of terrorists and saboteurs who are motivated by hatred,'' the report said. It also urged citizens to cooperate with the authorities to restore security in the country which has been rocked since Thursday by protests against the regime of strongman Moamer Kadhafi. State television separately showed what it said was ``live footage'' of pro-Kadhafi protests taking place at the landmark Green Square in central Tripoli.