A violent clash on Wednesday between students and security forces left many students injured, some seriously, at the main university in the Niger capital Niamey, a student leader said.The students were protesting to demand the reinstatement of five classmates who were expelled last month after being accused of assaulting a professor, students and residents told AFP."The clashes between the two sides were violent around the campus and inside," a resident of the neighbouring Lamorde district said.Student leader Salha Kaila told AFP by telephone: "We barricaded the road that goes in front of the campus, and the security forces burst onto the campus. There are many injured among our classmates."He said "some of the injured are fighting for their lives" at a university hospital in Lamorde. "For now... there is a precarious calm," Kaila added.The clash came a little over a week after a protest turned violent and a student died in unclear circumstances.The secretary general of the student union UENUN, Sita Diabiri, said on Tuesday that students had returned to class on Saturday after calling a "truce" to allow for negotiations with the government.Diabiri said their "main demand" was the reinstatement of the five students, including himself, who were expelled in March.They also want the university to reverse a decision to allow security forces to patrol the campus instead of UENUN.On April 9 hundreds of students demonstrated to demand better living and studying conditions in a protest that paralysed traffic as demonstrators set up barricades of tree trunks, blocks of stone and burning tyres.Security forces used tear gas to disperse the demonstrators, who responded by throwing stones.One protester died after a fall which authorities said was not linked to police action, but UENUN insisted the death was a result of the student having been hit by a police tear gas cannister. An inquiry has been opened.The university was paralysed by a month-long teachers' strike over the alleged assault on a teacher by students on February 7.The strike ended on March 17 after the five students were expelled and the university tapped the security forces for campus security.The students said there had been a "minor altercation" rather than an assault and slammed the expulsions as "unfair, disproportionate, illegal and arbitrary".President Mahamadou Issoufou held talks with student leaders in a bid to defuse the crisis.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.