New York - Renewed clashes in the Central African Republic are early warning signs of genocide, the UN aid chief said Monday, calling for more troops and police to beef up the UN peacekeeping mission in the strife-torn country.At least 180 000 people have been driven from their homes this year, bringing the total number of displaced in the Central African Republic to well over half a million, said Stephen O'Brien."The early warning signs of genocide are there," O'Brien told a UN meeting following his recent trip to the Central African Republic and the Democratic Republic of Congo."We must act now, not pare down the UN's effort, and pray we don't live to regret it."O'Brien said it was time to authorize an increase in troops and police serving in the Minusca force to enable the mission to "deliver on its critical protection mandate."The UN peacekeeping chief Jean-Pierre Lacroix last week said he was considering sending a request to the UN Security Council for more troops for Minusca.Military intervention One of the world's poorest nations, CAR was pitched into a war between Muslim and Christian militias in 2013. It was unleashed when President Francois Bozize was overthrown by a coalition of Muslim-majority rebel groups called the Seleka.They in turn were ousted by a military intervention led by former colonial ruler France. Those events sparked some of the bloodiest sectarian violence in the country's history as mainly Christian militias sought revenge.Christians, who account for about 80% of the population, organized vigilante units dubbed "anti-balaka", a reference to the machetes used by the Muslim rebels.The United Nations has 12 350 troops and police on the ground to help protect civilians and support the government of President Faustin-Archange Touadera, who was elected last year.While Touadera's government remains in control in Bangui, its authority is weak outside of the capital where former Seleka groups and anti-balaka fighters have clashed.'The risks are extremely high' Nine Minusca peacekeepers have been killed this year, raising alarm that the country is sliding back to the bloodletting that exploded in 2013 following the overthrow of Bozize.O'Brien said he was horrified by a visit he made to a Catholic church in the southern town of Bangassou where 2 000 Muslims took refuge three months ago, surrounded by anti-Balaka Christian fighters who are threatening to kill them. "The risks are extremely high and we must focus properly on whether to relocate them to another site or not," he said.Half of the country's population, or 2.4 million people, are in need of food aid to survive, the largest population in need per capita, he said.The country is also home to half a million refugees. "The risk of a relapse into another large-scale humanitarian crisis is imminent," said O'Brien.The United Nations has received only 24% of the $497 million it has requested in a humanitarian appeal for the Central African Republic.