Unknown gunmen have killed three Egyptian police officers in the north Sinai town of el-Arish as the Egyptian military continues an offensive against militants in the restive peninsula.

The three were killed after gunmen opened fire on a police station in el-Arish on Friday.

Earlier, Egyptian military helicopters targeted militant hideouts in several villages in the Sinai Peninsula as part of a mop-up operation against al-Qaeda-linked groups in the region.

The operation came two days after six soldiers were killed in two car bombings in Sinai. Ten soldiers and seven civilians were also wounded in Wednesday's blasts which were claimed by a militant group called Jund al-Islam.

Nearly 30 militants are reported to have been killed since military operations began in northern Sinai on September 7.

The Sinai has long been considered a safe haven for militants who use the region as a base for terror activities. In recent months, the remote desert region has been the scene of growing violence and militant attacks on security forces.

On August 19, militants ambushed a police convoy in the northern region of Sinai. At least 25 policemen were killed in the attack, which took place close to the town of Rafah. It was one of the deadliest attacks on security forces in decades.

In August 2012, sixteen Egyptian soldiers were killed in an attack on a police station near the border with Gaza.

In response, Cairo launched an offensive against terrorists in Sinai, sending thousands of troops backed by tanks and heavy equipment into the region.