Security forces raided the offices of CNN, Reuters and the Japanese national broadcaster NHK, all in the same building, CNN reported.
Reuters bureau chief Crispian Balmer said one staffer was assaulted with an iron rod and another was threatened with being tossed out the window. The attacks were followed by a protest sit-in by foreign journalists and a threat to boycott Hamas press events.
The offices were raided right after uniformed and plainclothes officers smashed a small student rally calling for unity between Hamas and its Palestinian rival, Fatah.
It was the second time in a week that Hamas has attacked media covering demonstrations in Gaza.