Tunisians are heading to vote for a president in a runoff between a symbol of the country's previous regimes and a veteran human rights activist that came to power after the revolution of 2011.

Sunday's runoff between the two candidates is the third election in the last two months and represents the final stage in the country's democratic transition. A parliament was elected in October.

The eve of the election was marked by violence with a shotgun blast wounding a soldier near the city of Kairouan. Extremists vowed further attacks on security forces in a video that surfaced on social networks Wednesday.

According to authorities, around 100,000 police and soldiers will secure the polls and certain stations in the border regions with Algeria will have shorter hours for security.