The government in Egypt is signalling that Christians can be attacked "with impunity" because of a new law that discriminates against the religious minority, human rights advocates are warning.

The new law, published by Al-Youm al-Sabaa, allows local authorities to forbid new church buildings and requires any new churches that are built to be "commensurate with" the number of Christians in the area.

It is also feared that the law's security provisions effectively sanction mob decisions against Christians.

Christian Today reported in August that the new law was being heavily criticised by the Coptic Christian community.

Now Human Rights Watch (HRW) is warning that the law discriminates against the increasingly-beleagured Christian minority in Egypt. 

There have been a number of recent incidents of mob attacks against Christians that have left one person dead, several injured, and properties destroyed.

Some of these incidents came in the context of Muslim anger about alleged church building. One recent YouTube video from a village near Alexandria showed people in the streets chanting: "We don't want a church."

"Even when authorities have made arrests, they have rarely prosecuted suspects, creating a climate of impunity for violent crimes that target Christians," said HRW.

Deputy Middle East director Joe Stork said: "Many Egyptians hoped that governments would respect and protect freedom of religion, including for Christians, after the 2011 uprising. Instead, the authorities are ignoring the underlying systemic issues and sending a message that Christians can be attacked with impunity."

Most Christians in Egypt are Coptic Orthodox and they are believed to make up between six and ten per cent of the 93 million population.

Egypt's constitution stipulates freedom of religion for Islam, Christianity, and Judaism but not for any other faith.