At least 12 people, including five Senegalese soldiers, have been killed after suspected rebels attacked an army base in the southern Casamance region.Five suspected rebels and two civilians died in the clashes, the army says.The BBC's Mame Campbell Toure in Dakar says the recent upsurge in fighting has shocked people, as it follows a long period of calm.The Casamance Movement of Democratic Forces (MFDC) has been fighting for the region's independence since 1982.A peace deal was signed with the largest rebel faction in 2004 and the level of violence had subsided.Once home to a thriving tourist industry, Casamance is separated from the capital, Dakar, by The Gambia. It is home to numerous ethnic groups, including many Christians, while northern areas are dominated by three, largely Muslim communities.One soldiers was killed when suspected rebels attacked a military base in Diegoune district, 45km (30 miles) north-west of Ziguinchor, the region's capital, near the Gambian border, at dawn on Tuesday, the army said.A vehicle carrying reinforcements was then attacked, leading to an "accident" in which a further four soldiers, including an officer, died, a statement said.The vehicle then crashed into a house, killing two civilians, it said.Unconfirmed reports say that nine soldiers were killed.Two weeks ago, five soldiers were taken hostage by suspected rebels - one of whom has since escaped. Analysts say the latest violence is linked to the elections due in February 2012.Some rebel factions are trying to extract concessions from the the government ahead of the poll, while others wish to transform the group into a political party, they say.Our reporter says the 29-year rebellion has become an important campaign issue, especially as army bases are now being targeted.