The leader of southern Sudan has called on his people to secede from the country in an upcoming referendum if they want to be free.

Speaking at a Sunday church service, Salva Kiir told worshippers in the southern capital of Juba that voting to remain part of Sudan would condemn them to being "second class citizens."

This is the first time Kiir has overtly called for seceding from the central government of which he is ostensibly a member.

The government dismissed his statements saying that Kiir has previously spoken strongly for maintaining the country's unity.

Two decades of north-south civil war ended with a 2005 peace agreement that called for a 2011 referendum to determine the future of the south.