Christian Solidarity Worldwide has deplored the "unwillingness" of Egyptian security services to protect Christians.
CSW chief executive Mervyn Thomas said it was "wholly unacceptable" that so little had been done to stop the killing of four Christians last week and a deadly attack on mourners who gathered for their funerals.
He called upon the Egyptian government to ensure "security, equality and fundamental freedoms to all of its citizens".
"It is time for words to be matched with actions in this regard," he said.
Morqos Kamel, 25, Victor Saad, 35, Mansour Attia, 45, and Essam Tawadros, 25, all Copts, died of gunshot wounds during a mob attack on 5 April in Khosous, a suburb 10 miles north of Cairo.
The attack followed unsubstantiated claims that Christians had daubed outrageous signs on the walls of an Islamic institution.
Two days later, mourners were attacked with stones and Molotov cocktails while coming out of St Mark's Cathedral, Cairo, where the funerals of the four men were being held. At least two people were killed and over 90 injured.
CSW's concerns echo similar statements from the head of the Coptic Orthodox Church in the UK, Bishop Angaelos who said security services had done "very little" to protect Christians from harm.
"It is now clear that the state needs to take that responsibility far more seriously," he said.