Thirteen Egyptian Coptic Christians detained after clashes with police have been released on humanitarian grounds, the prosecutor-general said.
Maher Abdel Wahed told reporters he had extended the detention of 21 others pending further investigations.
Policemen were injured when stones were hurled by protesters who had occupied the main Coptic cathedral in Cairo earlier this month.
Tensions between Christians and Muslims in Egypt have flared in recent weeks.
The protests began after rumours spread that a priest's wife, Wafa Constantine, had been abducted and forced to convert to Islam.
Government officials had said Mrs Constantine, 48, wanted to convert to Islam but was being prevented from doing so by her family.
The clashes at the cathedral ended when protesters were told that Mrs Constantine was back under the Church's protection.
Last week, Egypt's prosecutor-general said that Mrs Constantine had gone to police saying she wanted to change her religion, but had decided to remain a Christian after meeting Church officials.
Calm
The violence has prompted the Coptic Christian pope, Shenouda III, to go into seclusion at a monastery in protest at the treatment of Copts.
Also this month, police said they had arrested 25 people after sectarian violence erupted in the Upper Egyptian village of Munqateen.
Police were reported to be keeping Muslims and Christians apart after three Christian-owned shops and homes were attacked and police cars were wrecked.
Relations between the authorities and the Coptic minority - which makes up 5-10% of Egypt's population - are generally calm.
Copts remained the majority in Egypt for centuries after the 7th Century conquest of the country by Muslim armies.
In the modern age, they complain of discrimination in the workplace, restrictions on church construction and periodic fears that Christians are being forced to convert by Islamic extremists.