The attacker, named by police as 45-year-old Aleksandar Aco Martinovic, initially killed four people on Wednesday when he opened fire after a brawl at a restaurant in Cetinje.
He then shot dead eight people, including two children, at three other locations, prosecutor Andrijana Nastic said.
Police said the shooting was not thought to be connected to organised crime. (EPA PHOTO)
Martinovic was cornered by officers near his home in the town and tried to kill himself, then died of his injuries on the way to hospital in the early hours of Thursday, Interior Minister Danilo Saranovic said.
"When he saw that he was in a hopeless situation, he attempted suicide. He did not succumb to his injuries on the spot, but during the transport to hospital," Saranovic told Montenegro's state broadcaster, RTCG.
The incident is the second shooting in three years in the same town 40km west of the capital Podgorica.
In 2022 a gunman killed 10 people, including two children, before he was shot dead.
Police said Martinovic had been drinking heavily and had a history of illegal weapons possession.
After an altercation with patrons in the restaurant he went home, took a weapon, returned to the restaurant and started shooting, police said.
Four other people suffered life-threatening injuries during Wednesday's rampage, and one remains in a critical condition, Aleksandar Radovic, the director of the Clinical Centre in Podgorica, said.
Prime Minister Milojko Spajic said the shooting was a "terrible tragedy". (EPA PHOTO)
Police said Wednesday's shooting was not related to organised crime.
Montenegrin Prime Minister Milojko Spajic called the rampage a "terrible tragedy" and declared three days of national mourning.
President Jakov Milatovic said he was "horrified" by the attack.
Spajic said authorities would consider tightening criteria for owning and carrying firearms, including the possibility of a complete ban on weapons.
That will likely face opposition in Montenegro, which has a deeply rooted gun culture.
Despite strict gun laws, the Western Balkans composed of Serbia, Montenegro, Bosnia, Albania, Kosovo and North Macedonia, remain awash with weapons.
Most are from the wars in the 1990s, but some date even to World War I.
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