TRIPOLI (AFP) - Libya's prime minister on Thursday said the government had asked the United Nations and African Union to prepare and monitor a ceasefire, but ruled out the departure of strongman Moamer Gaddafi. "We have asked the United Nations and the African Union to set a date and specific hours for a ceasefire, to send international observers and take the necessary measures" to end combat, said Baghdadi al-Mahmudi. the Pentagon said Thursday that the NATO-led air war in Libya will cost the United States an estimated $750 million by the end of September. The estimate clarified an earlier statement this month by US Defence Secretary Robert Gates, who had cited the same figure without specifying if he meant the cost of the war to date or over the remainder of the fiscal year. Pentagon spokesman Colonel Dave Lapan told reporters the $750 million represents "the current estimate through the end of the fiscal year" on September 30. Earlier, African leaders gathered at a Libya-focused summit in the Ethiopian capital Addis Ababa called for an end to NATO air strikes to pave the way for a political solution to the north African nation's protracted conflict. But NATO insisted it would keep up its air raids in Libya until Gaddafi's forces stop attacking civilians and until the regime's proposed ceasefire is matched by its actions on the ground. "If the Gaddafi regime is serious about finding a solution, all it needs to do is end its attacks on civilians, withdraw its forces, and permit full, safe and unhindered access to humanitarian aid," a NATO official told AFP. African leaders on Thursday called for an end to NATO airstrikes on Libya to pave the way for a political solution to the conflict. The leaders made the call after a summit dedicated to Libya held at the African Union headquarters here. "As far as NATO airstrikes are concerned... you will see (in the summit declaration) a clear call by heads of state and government for those airstrikes to come to an end," said Ramtane Lamamra, AU Peace and Security Commissioner. "This is part of the requirement for political solutions to become possible," he said, adding: "The African Union shares the belief ... that what is taking place now goes beyond the scope of (UN resolutions) 1970 and 1973." But the head of the Libyan rebels' National Transitional Council delegation to the AU summit said the NATO strikes had prevented mass civilian killings by Moamer Gaddafi's regime. "If it were not for the NATO, we would have had massacres in Libya similar to those that happened in Rwanda," said Abdalla Alzubedi. "They have been mainly targeting military positions to protect civilians. Civilians are still under attack by the regime in so many cities all over Libya," he added, also calling for a peaceful solution to the crisis. The pan-African bloc also sought a stronger say in resolving the conflict. "Some international players seem to be denying Africa any significant role in the search for a solution to the Libyan conflict," AU Commission chief Jean Ping said at the start of the summit. "Africa is not going to be reduced to the status of an observer of its own calamities." The AU meeting wrapped up as the G8 summit got under way in the French seaside resort of Deauville. Ping expects to arrive in Deauville first thing on Friday, he told AFP in Addis Ababa. African heads of state attending the G8 will include South Africa's Jacob Zuma, Senegal's Abdoulaye Wade and Abdelaziz Bouteflika of Algeria, Ping said. The pan-African bloc has called for a Libyan ceasefire and set up a high-level mediation team, but its efforts have had little impact on the ground as Western powers continue with air raids against Gaddafi's regime. London-based daily The Independent reported on Thursday that the Libyan premier was sending international leaders a message proposing an immediate UN-monitored ceasefire in Libya. According to a letter seen by the newspaper, Gaddafi's regime was ready to enter unconditional talks with rebels, declare an amnesty for both sides and draft a new constitution. The Spanish government confirmed it had received a message to that effect. The NATO official, however, said the western alliance had received no such request and noted that the Gaddafi regime had made "similar statements" before, only to continue its attacks on civilians. "NATO will keep up the pressure on the regime until these steps are implemented in a credible, verifiable and sustained way," he said. Mahmudi, meanwhile, said previous "ceasefires announced by the regime have not been respected by any of the parties." This time the government wanted "all sides to stop fighting, especially NATO." He ruled out Gaddafi's ouster. "Moamer Gaddafi is in the heart of all Libyans. If he goes, they all go," he said, adding that the leader was "in good health" and operating without any restrictions on his movements.