Sudanese workers are refusing to go to work in an attempt to pressurise the ruling military government to make way for civilian rule.
The opposition called for a campaign of civil disobedience including a national strike, which began on Sunday.
Four people were killed after security forces fired tear gas and live ammunitions.
Monday remained quiet in Khartoum although some businesses started to reopen and a few buses were running.
Most shops, markets and banks in the capital, as well as in several other cities, remained closed as staff followed instructions from the Sudanese Professionals Association (SPA), the pro-democracy opposition, to not attend work.
The SPA called the strike after more than 100 peaceful protesters were killed by a paramilitary group, the Rapid Support Forces (RSF), on 3 June.
“The civil disobedience movement will begin Sunday and end only when a civilian government announces itself in power on state television,” the SPA said in a statement.
“Disobedience is a peaceful act capable of bringing to its knees the most powerful weapons arsenal in the world.”
Protesters have set up roadblocks across the capital. Social media users with access to a connection reported that the country’s internet was blocked by the ruling military government.
What’s the background?
The military took over Sudan after persistent protests led to the ousting of long-time President Omar al-Bashir in April. A military council promised a transition to civilian rule.
But pro-democracy campaigners say the military council cannot be trusted after Monday’s crackdown against a sit-in demonstration in Khartoum – and they have rejected an offer of talks.
In a separate development, three prominent opposition figures involved in mediation efforts were arrested after they met the Ethiopian prime minister, who was in Khartoum to try to restart peace talks.