Dozens of Hamas police and security forces on Wednesday entered Gaza City's Al Azhar university and began beating up students heading out for a protest, witnesses told AFP.
Sources inside the university said the security forces were dressed in civilian clothing and had targeted students heading out for a demonstration calling for national unity which was to have taken place at 11:00am (0900 GMT) in the Square of the Unknown Soldier.
At least 10 students were taken to hospital after being beaten by the security forces, and around 20 were arrested, university sources said.
Witnesses said the clash occurred when the police had forced their way into the university's administrative offices.
But a spokesman for the Hamas-run interior ministry denied that police had entered the university.
"What happened at the university was a problem between students," Ihab al-Ghussein told AFP.
However, witnesses and an AFP photographer at the scene said police were still blocking the gates, preventing anyone from leaving or entering the university premises.
Wednesday's demonstration, which had been called by a student group called "Enough," was organised a day after tens of thousands had taken to the streets of Gaza and the West Bank to demand that Hamas and the rival Fatah movement, which dominates the Palestinian Authority, end their bitter enmity.