The killings and attacks on journalists are "an egregious violation of international norms that uphold the media's right to conduct its work unmolested and without fear of violent reprisals," NPC President Angela Greiling Keane said in a statement Friday.
"It is critically important that both Egyptian security services and Muslim Brotherhood supporters respect press freedom and allow journalists to safely go about their work," she said.
The organization called on Egyptian authorities to investigate incidents in which journalists have been harmed or injured and to hold accountable those responsible.
Three journalists, including an employee of a government-run newspaper, were killed Wednesday, setting a record for the most journalists killed in a single day in Egypt. All of the journalists were covering a police crackdown at the Rabaa Al-Adawiya mosque in Nasr City.
A fourth journalist was killed at the mosque, although she was not on duty at the time.
Egyptian security forces shut down the offices of al-Jazeera Arabic Thursday night, the Committee to Protect Journalists reported Friday. Several al-Jazeera staff are already in detention or facing litigation.
Authorities have not revealed the whereabouts of a correspondent who was detained Wednesday, while the bureau chief and a broadcast engineer have been accused of threatening national security with their news coverage. A photographer has been jailed since July 15 on charges of gun possession.