US President Barack Obama and British Prime Minister David Cameron have said Libya’s Col Muammar Gaddafi must “relinquish power once and for all.” In a telephone conversation on Monday night the UK and US leaders agreed the crisis had “reached a tipping point”. They also reaffirmed the need for a peaceful transition of power in the country, a White House statement said. Rebel forces have taken control of large parts of Libya’s capital Tripoli, but Cameron warned there were still “difficult days ahead,” according to the (BBC). The UK prime minister and the US president also agreed on the importance of “avoiding civilian casualties” and establishing a “just and inclusive” system of democracy, said the White House.