OUAGADOUGOU, Aug 18 (Reuters) - Dozens of people were killed in northern Burkina Faso on Wednesday when Islamist militants raided a civilian convoy that was being escorted by military police, the latest in a spate of attacks across West Africa"s Sahel region this month. President Roch Kabore ordered three days of national mourning following the attack on the road between Gorgadji and Arbinda, one of Burkina Faso"s most volatile zones. Thirty civilians, 14 military police and three pro-government militiamen were killed, while 30 people were wounded, the government said in a statement. It added that 58 militants were killed in the ensuing clashes with security forces. Militants linked to al Qaeda and Islamic State regularly carry out attacks in Burkina Faso and neighbouring Mali and Niger, killing hundreds of civilians this year alone. Violence in the Sahel, a semi-arid band beneath the Sahara Desert, has continued to intensify despite the presence of thousands of U.N., regional and Western troops and efforts by some governments to negotiate with the militants. Armed men killed at least 12 soldiers last week in northwestern Burkina Faso as well as 30 civilians, soldiers and pro-government militiamen days before that. read more In Niger, armed men on Monday killed 37 civilians, including 14 children, in an attack on a village. read more The violence comes as former colonial power France prepares to begin drawing down its forces in the Sahel from 5,000 to about 2,500-3,000. The Sahel was thrown into chaos by the takeover in 2012 of northern Mali by militants linked to al Qaeda. France intervened the following year to push them back. But they have regrouped and expanded their operations, and they now threaten coastal West African countries like Benin and Ivory Coast. Reporting by Thiam Ndiaga in Ouagadougou Writing by Aaron Ross Editing by Matthew Lewis and Cynthia Osterman Our Standards: The Thomson Reuters Trust Principles.