The liberal Free Egyptians Party has condemned the "torture" of Egyptian Coptic Christians in Libya for allegedly proselytising.
Dozens of Coptic Christians were reportedly detained by Salafists following an attack on a church in Benghazi last week.
The statement on Tuesday condemned the "passive" response of Egypt's government and foreign ministry, and called on them to support Muslim and Christian Egyptians equally.
On Sunday, the Egyptian foreign ministry announced 20 of the Copts detained in Libya had been released and said it was negotiating the release of the remaining 22.
The incident could have a negative effect on relations between Libya and Egypt, the statement added.
The arrests are the latest in a series of recent incidents targeting Christians in Libya.
In December, two Egyptian Christians were killed and two injured when suspected Islamists threw a homemade bomb at a Coptic Orthodox church in western Libya.