A deputy principal at Al-Azhar, one of Gaza's largest universities, told journalists that police took over the university campus early Monday, denying entry to both students and university staff.
The official said he believed the refusal by the university's administration to hold a ceremony commemorating the life of Ahmed Yassin, the spiritual Hamas leader assassinated by Israel in 2004, was behind the take over.
The storming of Al-Azhar University will throw recent moves towards reconciliation and national unity between Fatah and Hamas into turmoil.
The two sides met last week the first time since a military coup last June, when Hamas, considered by many in the West as a terrorist organization, crushed Fatah troops and seized the Palestinian enclave.
Gaza has been in international isolation since, while the West Bank, where moderate Fatah maintains power, has resumed peace talks with Israel and received substantial aid from the West.
