The SPLM joined a power-sharing government in 2005 to end 21 years of conflict between north and south Sudan.

Tension in the country is rising ahead of elections due in April 2010.

They are the first presidential, parliamentary and local elections in 24 years. The government has declared Monday - the final day for voters to register - a public holiday in an effort to encourage voter registration.

On Sunday, about 20 opposition parties called for a gathering in front of the parliament building in the capital, demanding electoral reform.

On Monday security forces blocked roads leading to the parliament and arrested several protestors., according to the BBC.

A 22-year war between the mainly Muslim north and the Christian and animist south ended in 2005, after 1.5 million people died.

Semi-autonomous southern Sudan has been controlled by the SPLM since a peace deal in 2005 ended the civil war.

A referendum on whether the south should secede is due in 2011.