KHARTOUM (Reuters) - Security forces on Monday used teargas and batons to break up a third day of demonstrations in the Sudanese capital over the deaths of four students at a provincial university last week.

About 600 students rallied at Neelain University in downtown Khartoum, chanting "Killing a student is killing a nation" and "Revolution, revolution until victory", in the biggest protest since the students' bodies were found in a canal.

The protesters tried to march to a bus station in central Khartoum, but were stopped as security forces used batons to disperse them and made a number of arrests.

There was no immediate comment from police.

Arab-African Sudan avoided the mass protests that led to the downfall of rulers in Egypt, Tunisia, Yemen and Libya, but soaring food prices and other grievances have stirred smaller demonstrations over the past two years.

Riot police and other security forces also surrounded the University of Khartoum, where protests took place on Sunday and which has been the center of earlier anti-government demonstrations.

On Saturday, youth activists blamed authorities for the deaths of four students whose bodies were found dead in a canal at a university in an agricultural area south of Khartoum.

The Gezira University students were from Darfur, an impoverished western area the size of Spain that has been torn by war since insurgents took up arms there in 2003 complaining the central government had marginalized the region.

The students were demanding an exemption from tuition fees - as they say a presidential decree requires - when supporters of the country's ruling party broke up the demonstration, a spokesman for a Darfur student group said on Saturday.

The bodies of four of the students were later found in a canal, the group said.

Gezira state police confirmed the bodies of at least two students had been found but said there was no sign of violence.

The justice ministry has said it will set up a committee to investigate the incident.

Small protests erupted across the country in June after the government announced austerity measures to contain an economic crisis brought on by last year's secession of oil-producing South Sudan, but they withered under a security crackdown.

(Reporting by Khalid Abdelaziz; Writing by Alexander Dziadosz; Editing by Sophie Hares)