Two professors in the northwestern city of Rajshahi, who have in the past publicly criticised the army and the government, were arrested early on Friday, Altaf Hossain, head of the city's university, said.
He said intelligence officers told him they suspected the teachers of instigating the violence earlier this week that left one bystander dead and about 300 injured.
The detained academics were applied physics professors Saidur Rahman Khan, also a former head of the university, and Abdus Sobhan, leader of a left-leaning teachers' group.
Hossain said: "Their families said security forces in civilian dress picked up the teachers from their homes."
|"At least 10 army officers came to our house in the night and said that my father had to go with them to the police station"|
Dipannita, daughter of Dhaka University professor Anwar Hosain
In the capital, where the protests first began, security forces had earlier on Friday arrested two Dhaka University professors, Yusuf Haider, the school's acting vice-chancellor, said.
He said Harun ur Rashid, dean of the university's social science faculty, and Anwar Hossain, dean of bioscience and general secretary of the university's teachers' association, were arrested.
Dipannita, Hossain's daughter, said: "At least 10 army officers came to our house in the night and said that my father had to go with them to the police station."
The pair have been vocal in their criticisms of the army and the military-backed interim government, which took power seven months ago following a political crisis that saw the cancellation of national elections.
They had also been active in the protests this week, which began on Monday, when army personnel reportedly manhandled students during a football match on the Dhaka university campus.
Students then defied an existing ban on all protests - part of the state of emergency the government has kept in place for months - and demanded the army withdraw from the campus during a string of marches.
The students, many brandishing sticks, clashed with police who retaliated with tear gas.
Non-students joined the demonstrations, which quickly escalated into full-scale riots and spread across the country, despite a government decision to close the campus army post.
Protesters were demanding an immediate restoration of democracy and an end to emergency rule when the curfew was declared on Wednesday.
The measure temporarily shut down mobile phone services, cleared streets of protesters and forced people to stay home.
Violence subsided on Thursday as security forces patrolled the streets and the authorities warned they would take stern action against disorder.
All universities and colleges in the six cities, including the 40,000-student Dhaka University, have been closed indefinitely.