Al Arish, Egypt: Egyptian military aircraft struck suspected positions of Al Qaida-inspired fighters in villages of the Sinai Peninsula, killing 13 people, military officials said on Friday, in a stepped-up offensive after militants downed an army helicopter, raising concerns over an increasingly well-armed insurgency.

In the capital on Friday, two explosive devices detonated on a main highway on the western edge of the city, targeting a passing vehicle carrying riot police, Interior Ministry spokesman Hani Abdul Latif said. The blasts damaged the front window of the vehicle and wounded an officer, he said.

Nearby, security forces shot dead a minibus driver at a police checkpoint in the Sixth of October suburb of the capital. The police said the driver was trying to ram the checkpoint, ignoring warning shots, the ministry said. The driver was killed, one passenger wounded, and three others were arrested it said, adding that the incident was under investigation.

Around the country, riot police firing tear gas clashed with hundreds of supporters of ousted Islamist President Mohammad Mursi protesting in Cairo, the Mediterranean coastal city of Alexandria and Fayoum, south of the capital.

The military is battling Islamic militants in the northern part of Sinai who have escalated a campaign of bombings and shootings in retaliation for last summer’s army coup against Mursi and for the ensuing crackdown against Islamists.

The wave of violence, largely targeting Egypt’s police and security forces, has increasingly spread to other parts of the country — most lately, with two roadside bombs on Friday on the outskirts of the capital that wounded a policeman.

Overnight, explosions resounded for miles in the Sinai town of Shaikh Zuweyid near the border with the Gaza Strip, as Apache helicopters fired dozens of missiles, witnesses said. Military officials said the strikes targeted houses, shops, vehicles and other gathering points suspected of being used by militants.

Military spokesman Ahmad Mohammad Ali said 13 suspected militants were killed. The toll came from civilan agents reporting to the military on the burials of the dead at the town cemetery, the military officials said, speaking on condition of anonymity because they were not authorised to discuss the details.

The months-long military offensive in Sinai was stepped up after militants shot down a military helicopter on January 25, killing all five of its crewmembers. The Al Qaida-inspired group Ansar Beit Al Maqdis, or Champions of Jerusalem, claimed responsibility and posted a video of a fighter shooting and hitting a helicopter with a shoulder-fired missile.

It was not possible to verify the authenticity of the video but it corresponded with AP reporting.

The military officials said investigations have found that two Egyptians and four Palestinians were involved in the downing.

Since then, troops have stepped up their assault on the group. With the overnight strikes, 20 suspected militants have been killed the past week, one of the highest tolls since the offensive kicked off in the wake of Mursi’s July 3 overthrow.

Ali, the military spokesman, repeated the accusations on Friday, saying those killed in the overnight strikes were “extremely dangerous takfiri elements who are loyal to the Brotherhood terrorist group.” Takfiri is a term in Arabic referring to Islamic radicals.

In its latest statement on Thursday, Ansar Beit Al Maqdis claimed responsibility for the assassination on Tuesday of a senior police officer in Cairo.

Maj Gen Mohammad Al Said was shot to death as he left his home in the Haram district, a neighbourhood near the Pyramids. He was an aide to the interior minister and head of the technical office in the Interior Ministry, which is in charge of police.

In its statement posted on militant websites, Ansar denounced Al Said as “a renegade criminal” and warned the Egyptian military and police leaders to expect more attacks. “Expect the worst, as the time of punishment is near,” it said.

Separately, the group said it blew up a natural gas pipeline on Monday night outside Al Arish, the provincial capital of North Sinai. The attack, it said, was part of its war against the “Egyptian regime’s economy”. Gas pipelines have repeatedly come under attacks since the 2011 anti-Mubarak uprising and the security vacuum that ensued.