Twenty-two people have been killed and another 35 wounded in a bombing at Egypt's main Coptic Christian cathedral, according to Egyptian state television, in the second deadly attack to hit the Egyptian capital in two days.

Egypt's official Mena news agency said an assailant lobbed a bomb into a chapel close to the outer wall of St Mark's Cathedral, seat of Egypt's Orthodox Christian church and home to the office of its spiritual leader, Pope Tawadros II.

On Friday, six policemen were killed in a bomb attack in Cairo claimed by a group suspected by authorities of links to the outlawed Muslim Brotherhood.

There was no immediate claim of responsibility for Sunday's attack, which bore the hallmarks of Islamic militants fighting the government of President Abdel-Fattah el-Sissi.

As defence minister, el-Sissi led the July 2013 ouster of Mohammed Morsi, an elected Islamist president who hails from the Brotherhood.

Islamist militants launched a wave of attacks on security forces and Christians in response, as the government waged a sweeping crackdown on Morsi's supporters and other activists.