Security officials say 20 policemen were injured when their bus and armored personnel carrier were hit by a roadside bomb in the turbulent north of Egypt's Sinai Peninsula.

The officials say the bus carried policemen in civilian clothes as they left the town of al-Arish at the start of their leave. The armored carrier was their escort.

Most of the 20 injured policemen were lightly wounded, according to the officials, who spoke on condition of anonymity because they were not authorized to speak to the media.

Thursday's bombing came about a week after a coordinated attack by Islamic militants in northern Sinai killed 17 army soldiers, according to the Egyptian military. Officials in several branches of the security and military services say scores were killed in the July 1 attack.