BAMAKO, Dec 20 (Reuters) - Tuareg rebels attacked an army post close to Mali's border with Mauritania early on Saturday, a Malian military source said, testing a five-month ceasefire in Africa's third largest gold producer.

The source said gunmen in more than 20 four-wheel-drive vehicles raided the post at Nampala, some 400 km (250 miles) northeast of the capital Bamako before dawn.

"We think the death toll will be heavy because the post at Nampala is not enclosed," the source told Reuters.

"We think they are rebel chief Bahanga's men," he said referring to Tuareg insurgent chief Ibrahima Bahanga.

In July, Algeria brokered a ceasefire between Mali's government and the Tuareg rebels. For more than a year Tuareg fighters have attacked army posts and convoys to press for greater rights for their people in the largely desert West African country.

But doubts remain about the participation of Bahanga, a veteran rebel chieftain seen as something of a rogue element in the Malian Tuareg insurgency. (Reporting by Tiemoko Diallo; Writing by Daniel Magnowski; Editing by Katie Nguyen)

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