Khartoum, Sudan (CNN) -- Sudanese opposition leaders vowed Thursday to "topple the government" if their demands for political changes are not met.
"Our demand is to create an agreed-upon national government with a national program that solves all of our hanging issues," said Faruq Abu Issa, coordinator of the National Consensus Forces, at a rally.
The group is an alliance of major opposition political parties that was established in 2009.
Abu Issa also called for a "national constitutional conference to create a new democratic constitution."
If the ruling National Congress Party refuses, he said, "the leaders of the (opposition) political parties have decided that this regime should go and we will work to topple it."
Abu Issa and other opposition leaders hinted at using mass civil disobedience and strikes to achieve their goals.
The calls come just ahead of a historic vote in Southern Sudan. Residents of that region will begin voting January 9 on whether to stay in a united Sudan or separate and form a new country.
"We support the right of South Sudanese in their right for self-determination," Abu Issa added.
Among the other issues Abu Issa wants the government to address is the war in Darfur, public freedom laws and the rising prices of vital commodities such as sugar and gasoline.
Rabi Abd al-Ati, a senior leader of the National Congress Party, criticized the call to topple the regime as "unconstitutional."
"The current government was elected in a legal election," he said. "Unless there is a new election, we can agree on the peaceful exchange of power."
Sudan held its first multi-party elections in 24 years in 2010. Those elections, which led to the victories of President Omar al-Bashir and the National Congress Party, were boycotted by most opposition political parties.
The next elections are scheduled for 2015.
Abd al-Ati also called on opposition political parties to accept an offer made by al-Bashir last week to establish a "broad-based government."
So far, opposition parties have refused to take part.