Student supporters of Darfur rebel chief Abdelwahid Nur held anti-regime protests in Sudan on Wednesday, responding to a call from the exiled leader for nationwide uprisings to topple the Khartoum government.

"From today, as chairman of the Sudan Liberation Movement (SLM), I have ordered the people all around Sudan, and in Darfur, to rise and change... this Islamic and genocidal regime," Nur told AFP by telephone from Kenya.

In Nyala, the state capital of South Darfur, around 900 students demonstrated outside the university before they were surrounded by police, who fired tear-gas and drove them back inside the compound, a witness said.

Nur said there had been protests on Wednesday in all the main towns in Darfur, including El-Fasher and El-Geneina, although this could not immediately be confirmed.

He also repeated his call for the UN Security Council to impose a no-fly zone in Darfur similar to the one in Libya.

In Deleng, a town in the oil-producing border state of South Kordofan, around 600 student supporters of Nur's SLM marched, chanting slogans against Sudanese President Omar al-Bashir and state Governor Ahmed Harun, another witness said.

Bashir and Harun are both wanted by the International Criminal Court for alleged war crimes and crimes against humanity in Darfur, while Bashir has also been charged with genocide in Sudan's war-torn western region.

In the Sudanese capital, meanwhile, around 100 students from Al-Nilein University demonstrated outside the campus, shouting "Ocampo, you said the right thing!" in reference to the ICC's chief prosecutor Luis Moreno-Ocampo.

Security forces then arrived and arrested "many of them," according to a witness, who was unable to give details of the number of protesters detained.