Security forces in Sudan have arrested opposition leader Hassan al-Turabi from his home in Khartoum, al-Turabi's Popular Congress Party spokesman told Al Jazeera.
Monday's arrest comes a day after al-Turabi's party called for a "popular revolution" if the Sudanese government did not reverse price increases.
"He has been arrested ... with five other members of the group, and we don't know the reasons, because when they come to arrest him they don't give any reason," Bashir Adam Rahma, told Al Jazeera.
"Whenever this regime has a crisis ... they will capture Dr Turabi at first. I think they are afraid of him that he might instigate some kind of uprising because ... in Sudan there are no freedoms," Rahma said.
"This is a very bad situation economically, and due to the winds of freedom coming from Tunisia, any dictator in the region is looking to see from where the danger will come.
"If they arrest people, they think they can stay in power."
Earlier, al-Turabi said an uprising in north Sudan, similar to recent developments in Tunisia, was "likely".
"This country has known popular uprisings before," Turabi said in an interview to the AFP news agency.
"What happened in Tunisia is a reminder. This is likely to happen in Sudan ... If it doesn't, then there will be a lot of bloodshed. The whole country is armed. In the towns, it will be a popular uprising, but in Darfur, and in Kordofan as well, they have weapons."
Turabi has been in and out of jail since he left President Omar Hassan al-Bashir's ruling party in 1999/2000.