Gunmen killed a police officer Friday in northern Egypt who worked as a guard for a judge hearing a case against the country's ousted president as his supporters held scattered demonstrations that saw one person killed, authorities said.

The police officer had been riding a motorcycle in the Nile Delta city of Mansoura when gunmen on another motorbike opened fire on him, the Interior Ministry said in a statement on its official Facebook page.

A security official said the slain officer guarded a judge in one of four trials facing toppled Islamist President Mohammed Morsi. The official said the officer was killed on his way from the judge's home.

Officials also said they dismantled a homemade bomb on a main bridge in the north of Cairo.

A series of bombings and targeted killings, mainly striking security forces and installations, have hit the country since the military overthrow of Morsi in July.

Authorities largely blame the attacks on Islamic militants loyal to the ousted president. Violence initially surged last summer in the restive Sinai Peninsula before gradually spilling over into Nile Delta cities and the capital.

Meanwhile, hundreds of Morsi supporters took to the streets on Friday, the traditional Muslim day of prayer, to denounce the military-backed government and call on the release of their fellows detained during other demonstrations. They've been regularly protesting Friday since Morsi's overthrow.

A health official said one person was killed during a clash between Morsi supporters and opponents in the Mediterranean city of Alexandria.

During protests in Cairo, Suez and Alexandria, police fired tear gas to disperse demonstrators.

In the eastern Cairo district of Ain Shams, security officials said supporters of Morsi's Muslim Brotherhood group used firearms and set fire to tires and trash cans in clashes that wounded a police officer and a conscript.

All officials spoke on condition of anonymity as they were not authorized to speak to journalists.

Egypt's military-backed interim government has cracked down hard on Islamists after Morsi's ouster, detaining thousands of them while putting the group's top leadership on trial.