Suspected Islamist militants on Thursday shot dead a policeman at a military checkpoint in North Sinai's Al-Arish, security sources told state news agency MENA.

Islamist insurgents in the sparsely-populated peninsula, which borders the Gaza Strip and Israel, have intensified their attacks on police and military targets since the overthrow of Islamist president Mohamed Morsi in July, exploiting a security vacuum left by the 2011 uprising that toppled autocrat Hosni Mubarak.

On Wednesday, unknown assailants killed a 21-year-old police officer at a checkpoint between Rafah and Al-Arish. On the same day, gunmen opened fire at an armoured personnel carrier in the northern town of Sheikh Zuweid. No injuries were reported.

Also on Wednesday, security forces in Sheikh Zuweid discovered an underground field hospital treating insurgents and an arms cache, security sources told Reuters' Aswat Masriya.

The army has launched an unprecedented counter-terrorism campaign to quell an insurgency in the peninsula which has surged since Morsi's removal. More than a hundred militants have been killed and hundreds arrested, and a number of weapons depots belonging to insurgents have been destroyed.