Egypt's chief prosecutor has ordered the detention of six people suspected of involvement in the assassination of his predecessor last year.

In a Sunday statement, Nabil Sadek's office ordered the six, who were arrested a day earlier, to be held for 15 days pending investigation. Most are students at Al-Azhar, Sunni Islam's pre-eminent institution for religious learning.

A car bomb killed Hisham Barakat, who oversaw cases against thousands of Islamists, on June 29 as he left his home. It was the first assassination of a senior Egyptian official in 25 years.

The government responded by pushing through a wide-ranging anti-terrorism law that broadened the definition of terrorism, gave police greater powers of arrest, and tightened restrictions on free speech.