The incidents came amid ongoing tension in Lisbon, the capital, and in nearby towns and cities between police and some members of black communities who have accused officers of racist behavior. Authorities are investigating accusations that police needlessly and excessively beat a group of black people when they went to break up a fight in a low-income neighborhood last weekend. Police say they were responding to physical attacks on officers attending the incident.
Following that clash, neighborhood resident marched in downtown Lisbon but the gathering was marred by rock-throwing at police, who charged the troublemakers. Fires have been set in trash cans and cars have been torched this week in troubled neighborhoods with high rates of delinquency. Police have so far refused to link those incidents to the racial accusations, saying they could be merely acts of vandalism.
The juveniles, aged 16, 14 and 13, were detained Thursday night in Setubal, a city 50 kilometers (30 miles) south of Lisbon, where a bus was also torched during the night. An anti-racism group and a far-right movement are planning separate protests Friday, prompting concerns that tensions could escalate.
A group of 17 police officers from a precinct near Lisbon is currently on trial, accused of torture, assault, providing false statements and other crimes over alleged racist conduct. The alleged crimes refer to an incident in 2015, when police clashed with young black men in a poor neighborhood near Lisbon.
Many immigrants and their descendants from Portugal's five former African colonies live in poor suburban areas in the Lisbon region.