Sudanese security forces have fired tear gas at protesters who were taking part in pro-democracy demonstrations in the capital, Khartoum.
Teachers taking part in one protest were detained by the security forces.
Overnight demonstrators set up barricades for the first of two days of planned civil disobedience to protest against last month’s coup.
They are demanding the military government step back and allow a peaceful transition to civilian rule.
The demonstrations are happening as Arab League mediators arrive in Khartoum for talks to try to defuse the crisis.
The civilian Prime Minister, Abdalla Hamdok, remains under house arrest and is facing pressure from the military to co-operate with them, the BBC’s Andrew Harding reports from the capital.
Last month, the coup leader, Gen Abdel Fattah al-Burhan, dissolved the civilian arm of the government’s power-sharing agreement, arrested civilian leaders and declared a state of emergency.
Disruptions to the internet had left some people unaware of the two-day civil disobedience action but teachers turned out to protest near the education ministry.
“We organised a silent stand against the decisions by Burhan outside the ministry of education,” Mohamed al-Amin, a geography teacher, told AFP news agency.
“Police later came and fired tear gas at us though we were simply standing on the streets and carrying banners.”
In Khartoum North, security forces patrolled major streets carrying sticks and tear gas grenades, Reuters added.
‘The government is a killer’
There is anger on the streets of Khartoum today, with protesters blocking off neighbourhoods.
“Right now, there is a lot of blood, a lot of dead people. This military government is a killer,” one demonstrator told me.
In Khartoum’s private Royal Care hospital, many victims of the military clampdown are being treated.
It’s a place where support for the government is hard to come by.
“It’s heart-breaking to see those young people, the ones that have been killed, asking for what’s rightfully theirs: for a free country with a civilian government,” says surgeon Salma Elkhazin.
Despite these voices of concern, a spokesman for Sudan’s military government said the regime had done nothing wrong.
“Time will show this was not a coup,” retired Admiral Fateh al-Rahman told the BBC. “We will put a civilian government back in place and hold elections.”
The defiance of protesters here is simply impressive, and it’s possible that Sudan’s generals will back down amid growing international pressure.
But for now this country’s democratic revolution remains on hold – on a continent where it seems military coups are back in fashion.