Several thousand protesters charged at the Parliament building in downtown Podgorica, the capital, shouting "Milo Thief" and throwing various objects, including fire-bombs, at riot police guarding the site. The police then threw tear gas, chasing away the demonstrators with armored vehicles.
Witnesses said that several shop-windows were broken in the unrest, as tear gas smoke enveloped the city center.
Police said 15 policemen were hurt, while 24 protesters sought doctors' help because of tear gas. One opposition leader was detained.
Anti-government protesters gathered earlier at a central square, pledging to bring down the government. Opposition leader Nebojsa Medojevic shouted "the dictator must fall," referring to Djukanovic, who has been in power for 25 years and whom opposition accuse of authoritarian rule.
Some of the demonstrators carried banners reading "No to NATO" and "For military neutrality of Montenegro." Zoran Kovacevic, a 57-year-old unemployed electrician said that "we are against NATO, but most of all we are hungry."
Police also used tear gas twice last week against stone-throwing government opponents, who are also calling for early elections and a referendum on whether Montenegro should join NATO.
Montenegrin pro-Western government hopes to be invited to join the military alliance in December. Many Montenegrins with historic ties to Russia remain opposed.
The Adriatic nation of some 600,000 people split from a union with much larger Serbia in 2006.