KHARTOUM (REUTERS) - Security forces in the Sudanese capital Khartoum on Wednesday fired tear gas at demonstrators attending the funeral of a student killed in a protest, a Reuters witness said, and Khartoum University suspended classes "indefinitely".

Ali Musa was killed at a 200-strong protest march against escalating violence in the western Darfur region on the university campus when police fired tear gas at the protesters.

Police said on Tuesday they would investigate his death.

About a thousand people, some carrying flags and chanting "killing a student is killing the nation" and "revolution is the people's choice", marched in the procession. Some threw stones at police, and about five were slightly wounded.

"With the killing of this student, (President) Bashir has lost his legitimacy, and we'll go out to protest until we topple him," protester Hussein Yassin, 32, told Reuters.

Amnesty International condemned the killing and said security forces have "routinely used excessive force against mostly peaceful demonstrations over the last two years".

Dozens have been killed in Darfur in recent weeks in fighting between rebels and security forces. Critics accuse the government of war crimes and human rights abuses among ethnic minorities in the region.

President Omar Hassan al-Bashir has stayed in power despite rebellions, US trade sanctions, an economic crisis, an attempted coup and an indictment from the International Criminal Court on charges of masterminding war crimes in Darfur.

President Bashir faces a sharp drop in oil revenues, the main source of government income, and rising inflation after losing most of his active oilfields after the secession of South Sudan in 2011.

Subsidy cuts and other austerity measures brought in last September to cope with the crisis led to the capital's worst street protests in years, compounding the turmoil in a country also fighting rebels in southern and western border regions.