University students threw rocks at police in Kenya’s capital Tuesday as authorities fired back with tear gas in running battles that didn’t end until police cornered students in a campus building and fired dozens of rounds of tear gas inside, witnesses said.

Students demonstrated in at least four cities across the country over a proposed increase in university fees. But the protest by students from the University of Nairobi, was the most violent.

An Associated Press photographer said that several hours into the back-and-forth exchanges, police chased the students into university classrooms and fired tear gas inside, not even letting innocent students leave the gas-filled rooms.

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