Colonel Shamil Ahmad, head of Mosul's city hall police department, said rockets hit walls outside the hall at around 11:20am (08:20 GMT).
A child, two policemen and 10 other civilians were injured in the attack in northern Iraq's main city.
Ahmad said at least three attackers launched two Katyusha rockets from a locally made rocket launcher. Police found the launcher nearby, but nobody was arrested.
Earlier, a roadside bomb exploded in central Baghdad, badly damaging a vehicle and injuring at least five people, witnesses said.
Gunfire rang out immediately after the blast, which was strong enough to smash windows in nearby houses.
There was blood on the front seats of the large four-wheel drive vehicle, similar to those used by the US military and foreign security firms.
Shattered glass and a blood-stained cigarette packet could also be seen.
"Five Iraqis were wounded and one vehicle destroyed in an improvised explosive device attack on a civilian convoy in central Baghdad at around 07:44am (04:44 GMT)," a US military spokesman said.
According to Aljazeera's correspondent in Baghdad, the five were employees of the occupation authorities.
The correspondent said the explosion may have taken place in the Green Zone, the name given to the central Baghdad area where US forces are based.
The zone also came under intensive rocket-propelled grenade attack late on Friday, the correspondent said. Columns of smoke were seen in the area, he added.
A vehicle was damaged in the
The correspondent also reported that the al-Muthana airport, a US military base, came under intense missile attack late on Friday.
Also on Friday, a US marine, an Iraqi cameraman and at least six other civilians were killed in running battles between US troops and fighters in the flashpoint town of Falluja, west of Baghdad.
The marine's death took to 400 the number of US troops killed in hostile action since the start of the war last March to oust Saddam.
Also on Saturday angry unemployed protesters threw stones and lobbed grenades at the public job centre in the south-eastern Iraqi city of Amara on Saturday, forcing British troops to intervene, police said.
About 500 people gathered outside the building, part of the social security directorate in Amara, 365km southeast of Baghdad, the sources said.
Unemployed Iraqis demand
jobs and denounce 'bribes'
"The protestors threw stones and sound grenades at the building where police forces had been deployed," Police Captain Shahid Abid Ali al-Tamimi said. "Windows were shattered," he added.
Al-Tamimi said police forces then withdrew from the building to let British troops take control of the area as occupation forces' helicopters hovered overhead.
One of the protesters, Kazim Hussain Jabir, 24, said the demonstration was meant to demand jobs and denounce cases of "bribes paid to public employees to secure jobs".
On 10 January, six people were killed and eight others wounded in similar protests in Amara after British forces opened fire on armed men during the demonstration.
Unemployment is a major problem in Iraq, with some putting the jobless rate at 50% of the population.