CAIRO — Six people were killed in political violence on Friday as a small and little-known Islamist group’s call for protests failed to turn out big numbers but still spooked the military-backed government into locking down the capital.

The reaction betrayed a measure of official anxiety over the smoldering insurgency centered in North Sinai, but spilling to other parts of the country.

Violence was reported at levels only slightly higher than what has become usual in recent months. State media reported that two senior military officers were killed in separate drive-by shootings, one in Cairo and another in the Nile Delta town of Qalyubia. A police conscript was killed in Giza, across the Nile from Cairo.

Security officials said that at least three protesters were killed in clashes with the police in Matareya, on the outskirts of Cairo, a frequent protest hot spot. Around the country, more than two dozen protesters were injured and more than 200 were arrested, state media reported. A few improvised explosives detonated without causing injury, and the police said they had defused as many as 10 more.