A man who was wounded in a mass shooting on New Year's Day in Montenegro has died, bringing the death toll to 13.

Thousands of Montenegrins gathered in the town of Cetinje on Sunday to commemorate the 12 victims of a mass shooting last week, with many accusing police of not having done enough to stop the gunman's rampage.

The New Year’s Day shooting shocked a country where gun ownership is widespread. Montenegro’s government began a three-day mourning period Thursday after a gunman opened fire on New Year’s Day — killing 12 people, including two children, across several locations.

Several thousand people have participated in street protests in Montenegro. The demonstrators on Sunday demanded the resignations of top security officials over a shooting earlier this week that left 12 people dead including two children.

STORY: A gunman who killed several people in a small Montenegrin town on Wednesday, has died from self-inflicted injuries.That's according to police hours after the shooting.It is one of the tiny Balkan nation's worst mass killings.

Aco Martinović, the alleged shooter from the town of Cetinje in southern Montenegro, died on the way to the hospital after attempting suicide earlier. His actions resulted in the deaths of 10 people and injuries to 4 others.

The government has declared three days of national mourning from Thursday, with Prime Minister Milojko Spajic saying the shooting had "shrouded our country in black". Police said the attack began at 17:30 local time (16:30 GMT) when a man - named as Aleksandar Martinović, 45 - opened fire in the restaurant.