"Shelling of Boko Haram around the northern axis of the state was going on," the source told The Anadolu Agency on Saturday.
He said the shelling aimed to foil attempts by Boko Haram militants to launch an attack into the city.
"What you're hearing is not bomb but shelling from our troops because the insurgents are still desperate to attack Maiduguri," he said.
Heavy shelling and shooting were heard in the early hours of Saturday in the outskirts of Maiduguri.
"The shooting started at about 5.30am (local time) and sounding like bombs," Dauda Mbaya, a local resident, told AA.
The shelling has created a state of panic among residents with many presuming that Boko Haram was making attempts to storm into the city.
"I was scared when the shooting persisted. I thought Boko Haram was attacking the city again following speculation the insurgents may strike b weekend," Julius Emmanuel, a local resident, said.
Boko Haram launched simultaneous attacks on Maiduguri on Sunday in an attempt to capture the provincial capital.
The insurgents have captured a major army barrack in Monguno, about 135 kilometers from Maiduguri.
For the last five years, Nigeria has battled a fierce Boko Haram insurgency that has ravaged the country's volatile northeast and claimed thousands of lives.
The year 2014 proved to be the insurgency's bloodiest year yet, with increasingly frequent attacks, higher death tolls and a deluge of displaced persons.
A seemingly emboldened Boko Haram recently stepped up its militant activity, seizing several areas of Nigeria's Adamawa, Yobe and Borno states, where it has since declared an "Islamic caliphate."
The violence displaced well over 1.5 million people in 2014, according to a recent report by the Borno State government.