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SEGOU, Mali -- The French military says its fighter planes and helicopter gunships have carried out a dozen operations over the weekend in Mali, most of them aimed at "terrorist vehicles."

The report came late Sunday as Mali's president thanked France for its military support in ousting the Islamists from some of their strongholds in northern and central Mali.

France said some 400 troops from Nigeria, Togo and Benin had arrived Sunday in Bamako.

Troops from Chad, who are considered hardened fighters familiar with the desert-like terrain of northern Mali, also arrived in Mali.

France launched its military offensive on Jan. 11, but has said that African nations must take the lead.

A top official with the West African regional bloc said Sunday the cost of the African intervention could top $500 million.