A U.N. peacekeeping force Monday took over security duties in Mali from an African-led peacekeeping mission as the country prepares for a presidential election later this month.

In a ceremony Monday, most of the 6,000 African troops became part of the U.N. force, six months after they first deployed to help the Malian army fight the Islamists who seized control of the country's north, the Voice of America reported.

The U.N. Security Council has authorized a one-year mission with up to 11,200 military personnel and 1,440 international police, making it one of the largest U.N. peacekeeping missions.

U.N. peacekeeping chief Herve Ladsous visited the city of Timbuktu Sunday ahead of the transfer. He met with political and religious leaders and toured a UNESCO World Heritage site.

Last week Ladsous told the U.N. Security Council that the new U.N. mission poses "unique challenges" to peacekeepers because of Mali's climate, infrastructure and size.

Mali plunged into chaos last year when soldiers overthrew the government, allowing ethnic Tuaregs and later al-Qaida-linked militants to take over the north. French and African troops helped drive the Islamists from major towns.

The U.N. Security Council has authorized Secretary-General Ban Ki-moon to request French military intervention if U.N. troops in Mali came "under imminent and serious threat."