Egyptian police arrested five men accused of involvement in the bombing of a police bus in the northern governorate of Beheira last month which killed three police conscripts and injured 27 others.
The interior ministry said in a statement that the attackers "aimed to drive a wedge between the police personnel and the interior ministry, as the explosion took place at the same time as the Sharqiya police personnel protest."
Lower-ranking police had protested in the northern governorate of Sharqiya for two days in August over low salaries and working conditions.
Egypt has been battling a growing Islamist insurgency since the 2013 ouster of Islamist president Mohamed Morsi.
The attacks are concentrated in the northern Sinai Peninsula but have also extended to the mainland.
Most attacks have targeted security forces.