A third policeman has died from Saturday's blast in Mahalla, the largest city in the central Nile Delta, state news agency MENA reported on Sunday.
Abdel-Kareem Mohamed, 50, succumbed to his injuries in hospital, a local health ministry official said.
A policeman and an army conscript were killed in the early hours of Saturday when an explosive device detonated in the Delta city.
The policeman had been on guard duty outside Emirates NBD bank near the site of the explosion. He died immediately on the scene.
The other victim, a 25-year-old conscript, was accidentally passing near the site of the explosion. He succumbed to his injuries a few hours later, Health Ministry deputy in Gharbiya Mohamed Sharshar told MENA.
The explosion, which took place on Shokry Al-Qawatly Street, left 16 others injured, according to the ministry of health.
The injuries ranged from burns to bruises and leg amputation.
The ministry of health said that four of the injured were in a critical condition.
Egypt has been facing a decade-long Islamist insurgency in the Sinai Peninsula, which spiked after the ouster of Islamist President Mohamed Morsi in July 2013.
Militants have repeatedly attacked police and army sites and personnel in Sinai as well as other parts of the country, leaving hundreds dead and injured.
In recent months, militants have increasingly attacked economic targets in urban areas, such as electricity pylons and mobile-network stores.
Civilians have often fallen victim during various violent attacks.
New Interior Minister Magdy Abdel-Ghaffar has announced a security plan ahead of the international investment summit scheduled to take place in resort town of Sharm El-Sheikh on 13-15 March.