A march in support of unification with Moldova turned violent in the Romanian capital after several people broke through riot police lines trying to reach a symbolic downtown site.
A police spokesman told local television that five people were detained in the scuffles, which took place outside the main government building in Bucharest on October 22.
There were no immediate reports of injuries, though local media reported that bottles and sticks were thrown at police.
The march, attended by an estimated 2,000 people, had been authorized by Romanian officials and proceeded largely without incident until a group of people broke away from the main crowd and tried to reach University Square, a site with powerful symbolic value.
A march organizer, George Simion, was reportedly among those detained, though a police spokesman declined to confirm that.
Simion, a Romanian citizen, had twice been expelled from Moldova for his activities, but each time Chisinau lifted the order barring him entry.
Local television stations reported that the five detained were fined 3,000 lei ($725) each for disturbing public order and released.
A small crowd waving Romanian and Moldovan flags later regrouped in University Square as darkness fell.
The square was the site of anticommunist protests in December 1989, and thousands held a months-long protest in 1990, which was later quashed in a violent attack by miners called in by the government of then-President Ion Iliescu.
Many of those marching earlier were Moldovans who study in Romania, but some were also believed to be older Moldovan citizens who traveled from the Moldovan capital, Chisinau.
Alina Ieremciuc, another organizer of the event, told Romanian media that the march was largely peaceful, and he condemned the violence.
The issue of unifying Moldova with Romania is deeply controversial, particularly in Moldova where a sizable part of the population is Russian-speaking. Most of present-day Moldova was part of Romania before World War II.
During the breakup of the Soviet Union, Moldova's mainly Russian-speaking region of Transdniester broke away following a short war that killed some 1,000 and was eventually quashed by Russian troops.
Russia still keeps a contingent of troops ostensibly as peacekeepers in Transdniester, whose status remains a flashpoint, both for Moldovan nationalists as well as Russia.
The pro-unification march comes just more than one week ahead of a presidential election in Moldova, where a pro-Moscow candidate is currently leading in polls.
In recent years, Moldova -- one of Europe’s poorest countries -- has struggled over the question of whether to deepen its economic and trade ties with the European Union. Russia opposes that, which has led to fears of a full-blown conflict erupting, similar to what happened in Ukraine in 2014.