Sudanese police beat and arrested students on Sunday as protests broke out throughout Khartoum demanding the government resign, inspired by a popular uprising in neighbouring Egypt.
Hundreds of armed riot police broke up groups of young Sudanese demonstrating in central Khartoum and surrounded the entrances of four universities in the capital, firing teargas and beating students at three of them.
Police beat students with batons as they chanted anti-government slogans such as "we are ready to die for Sudan" and "revolution, revolution until victory".
Groups have emerged on social networking sites calling themselves "Youth for Change" and "The Spark", since the uprisings in nearby Tunisia and close ally Egypt this month.
"Youth for Change" has attracted more than 15,000 members.
"The people of Sudan will not remain silent any more," its Facebook page said. "It is about time we demand our rights and take what's ours in a peaceful demonstration that will not involve any acts of sabotage."
The pro-democracy group Girifna ("We're fed up") said nine members were detained the night before the protest and opposition party officials listed almost 40 names of protesters arrested on Sunday. Five were injured, they added.
Sudan has a close affinity with Egypt - the two countries were united under British colonial rule. The unprecedented scenes there inspired calls for similar action in Sudan, where protests without permission, which is rarely given, are illegal.
Before Tunisia's popular revolt, Sudan was the last Arab country to overthrow a leader with popular protests, ousting Jaafar Nimeiri in 1985.
Opposition leader Mubarak al-Fadil told Reuters two of his sons were arrested on their way to the central protest. Editor-in-chief of the al-Wan daily paper Hussein Khogali said his daughter had been detained by security forces since 8 am (0500 GMT) accused of organising the Facebook-led protest.