Fatah had called for its supporters to assemble at the Unknown Soldier square as a peaceful protest against Hamas's control of the Gaza Strip, but the gathering turned into a rally.
When several Hamas security men roughed up a Reuters TV cameraman filming the protest and tried to confiscate his camera, protesters surrounded the Hamas men, beat them to the ground and prevented the cameraman's arrest.
The Hamas men also detained a photographer working for the AFP news agency and a cameraman for the Russian TV channel Russia Today, along with two other reporters working for local news outlets.
They further broke a TV camera belonging to the Arabic-language TV network Al Arabiya.
All four detained journalists were quickly released, Hamas officials and witnesses said.
They said they got their equipment back. Later, journalists staged a separate protest against the crackdown.
Khaled Bolbol, one of the local reporters detained, said he was abused and ordered to speak to Hamas' al-Aqsa television station.
"I refused," he said. "I was beaten and stepped on ... I don't want to speak to (Hamas) TV or any other."
Islam Shahwan, spokesman for the Hamas force, accused a small group of Fatah activists of "inciting chaos and bringing back the situation to lawlessness".
He said Hamas "will not allow the situation to be repeated" and promised to arrest those behind the protest.
However, a Fatah official said: "The events today are a clear sign that Fatah did not vanish with the Hamas coup.
"People are against Hamas suppression of Fatah. Hamas thought it can eliminate Fatah, they are wrong. Fatah is rising again".