The Sudanese Professionals Association, an umbrella group of independent professional unions, has been spearheading anti-government protests that erupted in December over spiraling prices and a failing economy, AP reported.
Demonstrations quickly turned to calling for President Omar al-Bashir's departure after nearly three decades in power.
Saturday's marches come on the 34th anniversary of the overthrow of President Jaafar al-Nimeiri in a bloodless coup.
The military removed Nimeiri after a popular uprising in 1985, before handing power over to an elected government, which in turn lost power to Bashir in a coup supported by his hard-liner allies.