Former Nigerian President Olusegun Obasanjo arrived in Senegal late Tuesday to head a joint election observation mission between the African Union and the Economic Community of West African States .

When asked what message he brought to Senegal from the AU, President Obasanjo said his first job is to observe Sunday's vote and his second job is to be proactive on behalf of AU and ECOWAS, to prevent what is “undesirable and unwanted.”

His arrival coincided with yet another day of violence in the Senegalese capital, Dakar. Police dispersed an opposition demonstration with tear gas before the protesters could reach the city's center.

The opposition is calling for incumbent President Abdoulaye Wade to withdraw his bid for a third mandate, citing a constitutional reform in 2001 that limits presidents to two terms.

Anti-government protests have so far claimed six lives. Senegal's opposition has called for international intervention to encourage Mr. Wade to step down and prevent further violence.