Updated

The U.N. Security Council on Thursday unanimously approved a nearly 12,000-strong U.N. peacekeeping force for Central African Republic, which has been torn by mounting violence between Christians and Muslims.

The 10,000 U.N. troops and 1,800 police will take over from 5,000 African Union soldiers -- but not until Sept. 15.

A separate 2,000-strong French force in the Central African Republic was authorized to use "all necessary means" to support the new U.N. force.

Central African Republic has been in chaos since a March 2013 coup, when mostly Muslim rebels seized power and launched a brutal regime. Christian militiamen attacked rebel strongholds in early December. As the rebel government crumbled in January, the Christian militiamen stepped up the violence, forcing tens of thousands of Muslims to flee.

The resolution expresses serious concern at multiple violations of human rights and humanitarian law committed by both former Seleka elements and anti-Balaka militia including killings, torture and sexual violence against women and children.

The resolution "demands that all militias and armed groups put aside their arms, cease all forms of violence and destabilizing activities immediately and release children from their ranks."

The Security Council wanted a strong mandate and the resolution authorizes the new U.N. force to protect civilians and support the disarmament of combatants and the restoration of peace and law and order. It also authorizes the mission to help investigate violations of human rights and humanitarian law by armed groups.

While U.N. peacekeepers and police will not take over until Sept. 15, the resolution immediately establishes the U.N. mission, to be known as MINUSCA. It will take over all activities of the U.N. political office.

The resolution also urges the transitional authorities to accelerate preparations for free and fair elections no later than February 2015.

With the establishment of MINUSCA, the African Union force on the ground will receive logistical support from the United Nations. Many of its members are likely to become part of the new U.N. force after being checked to ensure they meet U.N. standards.