Associated Press
A helmet and a weapon of the Egyptian security forces are placed at a barricade as they prepare to watch the area in Beni Sueif, south of Cairo, Egypt, Friday, Aug. 30, 2013.

EL-ARISH, Egypt — Suspected militants killed an Egyptian police officer Friday in the Sinai Peninsula, a security official said, as authorities stepped up security measures ahead of scattered protests by supporters of the country's ousted Islamist president.

Near-daily attacks against Egyptian police and soldiers in the restive northern Sinai increasingly resemble a full-fledged insurgency. The army has launched an operation to quell violent incidents against its troops there.

In Friday's attack, gunmen opened fire at the police officer as he walked near his home in the city of el-Arish, an Egyptian security official said. He spoke on condition of anonymity because he was not authorized to speak to journalists.

Meanwhile, supporters of ousted President Mohammed Morsi held demonstrations around the country to protest against the military-backed interim government and its crackdown on the Muslim Brotherhood.

Thousands of protesters marched in the Mediterranean city of Alexandria. Rallies also were held in several suburbs of Cairo, including in the working class district of Helwan, south of the Egyptian capital.

Authorities tightened security around the country's constitutional court in southern part of Cairo, where the Brotherhood leaders had asked supporters to protest Friday.

Armored vehicles and barbed wires sealed off several of the capital's major squares, sites of previous protests. They included Tahrir Square, the epicenter of Egypt's 2011 uprising that forced longtime autocrat Hosni Mubarak from power.

Morsi's supporters repeatedly have tried to rally at Tahrir following the July 3 military coup that toppled Morsi and the Brotherhood-led government.

Security, already volatile since 2011, has worsened since the military overthrew Morsi following mass protests calling for his resignation.

The interim government has launched a major security crackdown on the Brotherhood, arresting nearly 2,000 members, charging its top leaders with inciting murder and violence, and breaking up demonstrations by Morsi supporters with what rights groups call excessive force that has killed hundreds. Morsi himself remains held at an undisclosed location.

The crackdown has not prevented Morsi supporters from holding near-daily protests demanding his return. However, fewer now attend since they regularly descend into violence. Clashes often erupt between the protesters and security forces and supporters of the military.