EL-ARISH, Egypt (AP) — Unknown assailants killed an Egyptian police officer in the restive northern Sinai Peninsula on Friday, as hundreds took to the streets in scattered protests against the military's ousting of the former Islamist president.

Militants have stepped up attacks against security forces in Sinai since Morsi's overthrow in July following mass protests calling for his departure. Morsi's supporters have been protesting his removal, despite a heavy security crackdown by the state. In mid-August, police broke up two major Islamist sit-ins in Cairo with a heavy hand, leaving hundreds dead.

According to an Egyptian security official, the young officer killed on Friday in the city of El-Arish was driving back home when two attackers opened fire on him and fled. He was found with twenty bullets in his head and his chest, the official said.

In a separate incident also in Sinai, militants struck two armored military vehicles with a roadside bomb, according to the official.

One soldier was injured in the explosion and was transferred to a local military hospital, the official said. He was speaking on condition of anonymity because he was not allowed to speak to the media.

Attacks against Egyptian security forces have taken place mostly in northern Sinai, prompting the army to wage a war there against local militants. Some attacks also occur in Cairo, however, and suspected Morsi supporters have attacked police stations, government buildings and churches in a string of provincial towns and cities.

On Friday, two policemen and two civilians were wounded when attackers riding a motorbike hurled a grenade at a police checkpoint in Qalioubiya province, north of Cairo, Egypt's state news agency MENA reported.

Meanwhile, Morsi supporters held scattered protests across the country denouncing the coup that ousted him. Their demonstrations have witnessed a sharp decrease in numbers since a heavy security crackdown left hundreds dead and thousands in jail. Most Brotherhood leaders have been arrested, including top leader Mohammed Badie. On Monday, the organization was banned by an Egyptian court that ordered its assets confiscated.

Friday, hundreds marched in the middle-class suburb of Helwan, south of Cairo, holding up yellow posters with the outline of a hand showing four fingers. Morsi supporters have used the symbol in online and street campaigns to remember the sit-in protest around the Rabaah al-Adawiya mosque, which in Arabic means fourth.

Clashes broke out between Morsi's supporters and opponents in the Mediterranean city of Alexandria, the website of the state-owned Al-Ahram daily newspaper reported. State radio said security forces intervened after Morsi supporters fired birdshot, arresting fourteen of them. MENA said clashes also broke out in another poor Cairo suburb.

Five people were also injured in similar clashes in the Nile Delta province of Damietta, Al-Ahram said.

Egypt's military-backed interim government is pushing a fast-track timetable for a return to democracy by amending the now-suspended constitution and holding presidential and parliamentary elections early next year.