Nine Egyptian policemen were wounded Monday when a bomb detonated on a road in North Sinai, near the border with the Gaza Strip, security sources in the country said.
The blast hit a police bus as it travelled from Rafah, a town on the Gaza border, to el-Arish, an hour's drive away.
Islamist militants expanded into a security vacuum in the region left by the downfall of ousted autocratic leader Hosni Mubarak in 2011.
Attacks on army and police have intensified since the military deposed Egypt's first Islamist president, Mohamed Mursi, on July 3 after mass protests against his rule. Since then, more than 100 members of the security forces have been killed in Sinai.
Last week, the army stepped up a campaign to restore control in the area. An army spokesman said on Sunday that the heavy weapons seized from militants in recent operations included anti-aircraft missiles.