Gao was the first city freed from Islamist occupation by a French-led military intervention that drove al-Qaida-linked fighters from the country's north earlier this year.
While it bore the brunt of the guerrilla-war waged by remnants of the defeated insurgents in the months following the January offensive, until Monday's violence the area had not seen an attack since May.
“This morning from around 06:30 [0630 GMT] a series of four explosions hit the town. One Malian soldier was wounded and a house was damaged,” Idrissa Cisse, a municipal official in Gao, told Reuters.
Cisse and Gao residents said Islamists had fired mortar bombs from outside the city, though a military official said the explosions had been caused by rockets.
“It was indeed jihadists who fired the rockets at the city. They are still in the region,” he said.
French helicopters were patrolling the skies above Gao by mid-morning, and residents said calm had returned to the city.
Mali's new President Ibrahim Boubacar Keita was elected in August having promised to make security a top priority as the country battles the remnants of the Islamist militant groups, which occupied the north of the country for over nine months.
At least four people were killed and several wounded in a suicide car-bomb attack in Timbuktu, another northern city previously occupied by Islamists, late last month.
While former colonial power France spearheaded operations earlier this year in the vast Sahel nation, Paris is now seeking to reduce its presence in Mali and hand over to a U.N. peacekeeping mission.
The United Nations has approved the force, expected to number about 12,600 soldiers and police officers once fully deployed, to help stabilize and secure the country.