Thousands of security cameras have been installed across Somalia's capital to monitor the movement of al Shabaab militants and reassure residents, but they have also made business owners fearful of reprisal attacks.

Rolled out this year as part of a municipal government initiative, officials say CCTV cameras have helped authorities keep track of militant activity in Mogadishu and ensure that security forces are doing their jobs properly.

The aim is to stave off the bombings and shootings that have plagued the capital in Islamist al Shabaab's nearly two decade-long fight to overthrow the government.

But in a city where militants have eyes and ears everywhere, some businesses who have installed cameras have themselves come under attack.

At least three people have been killed and four wounded in assaults on such businesses since the start of October in the Daynile and Hodan districts of Mogadishu, Mohamed Ahmed Diriye, a deputy mayor, told Reuters.

Several businessmen told Reuters that al Shabaab had ordered them to take down the cameras, but government officials have warned they could face consequences for doing so.

"We warn them against taking orders from terrorists," Diriye said after the latest attacks. "Anyone who removes the cameras will face the law."

Farah Aden, a shopkeeper in Daynile, said business owners had been left exposed to attacks by militants and felt trapped.

"There is new fear due to security cameras," he said. "We are in a dilemma. We are caught between two opposite directives."

But some residents welcome the new surveillance. Second-year university student Ahmed Ibrahim said the cameras offered reassurance to people going about their daily lives.

"In the past, it was difficult to attend school or college," he said. "There used to be explosions just outside the school or university campus and when going back home."

Samira Olow, 30, a mother of six who sells food in front of her house, said she was afraid of being caught in the crossfire when out in public.

"There is always fear in Somalia, and now fear in Mogadishu is due to security cameras," she said. "We go to shops to buy food and we can be at the shop when the shopkeeper is being targeted and this is dangerous."