The mission, approved by EU governments on Monday, will start work next month in the Niger capital Niamey.
The rebel takeover in the north of Mali, which borders Niger, as well as an influx of weapons and fighters after last year's revolt in Libya, have raised fears about the stability of the arid Sahel belt of central and west Africa, Reuters reports.
"Increased terrorist activity and the consequences of the conflict in Libya have dramatically heightened insecurity in the Sahel," EU foreign policy chief Catherine Ashton said.
"European experts will train (Niger's) security forces to improve their control of the territory and regional co-operation," she said in a statement.
About 50 international staff and 30 staff hired locally will be based in the mission's headquarters in Niamey, with liaison officers in Bamako, the capital of neighbouring Mali, and Nouakchott, capital of Mauritania.
The international staff will mostly be civilian security trainers from EU member states. The team will also have military expertise, EU officials said, but gave no further details.
Mali's March 22 coup precipitated the fall of the country's north to a mix of secular and Islamist rebels, who now control a desert region the size of France at the heart of the Sahara.
The rebel takeover has emboldened al Qaeda's north Africa wing, known as AQIM, as well as other foreign militants, including Nigerian fighters from Islamist group Boko Haram.
Officials in Niger, a major uranium exporter, said last month that plans for the EU mission had been brought forward because of the threat of militant attacks from Mali.
African leaders are seeking U.N. Security Council support for military intervention in Mali to end the rebellion in the north and reunite the Sahel state.
The European Union also approved a 23 million euro ($28 million) mission to help states in the Horn of Africa and Indian Ocean police their territorial waters to fight piracy off Somalia.
The plan involves Somalia, Djibouti, Kenya and the Seychelles and will be extended to Tanzania later.
Rampant piracy off Somalia has made the country's waters the world's most dangerous shipping lane, has secured Somali bandits tens of millions of dollars in ransoms and pushed up insurance premiums for ships.
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