Sudanese security forces have fired tear gas at dozens of teachers who were taking part in pro-democracy protests in the capital, Khartoum.
There are reports that many teachers 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.
