Police in southwestern Germany hit protesters with water cannons and pepper spray Thursday as they demonstrated against a railway project.
Organizers said thousands of protesters turned out at the rally in Stuttgart, but police spokesman Fritz Erlach said there were only about 1,500 to 2,000 demonstrators.
"There was massive resistance by the protesters," Erlach said. "We used water cannons and also pepper spray," he said, adding that some protesters threw stones at police.
State Interior minister Heribert Rech said more than 1,000 police officers were on hand.
Erlach had no information about whether anybody was injured, but German news agency DAPD reported clashes with police left dozens of people slightly hurt.
Axel Wieland, who heads the regional division of the environmental group BUND accused police of using "excessive violence."
"The use of water cannons, tear gas and pepper spray is unjustifiable because all protest participants were peaceful," Wieland said.
Erlach denied that tear gas has been used.
Protests against the euro4.1 billion ($5.5 billion) Stuttgart 21 project, which foresees moving the city's station underground, escalated Thursday as preparations were being made to fell 300 trees at the construction site.
A fence was built to surround the area and the situation calmed down, Erlach said.
"We are peacefully protecting those trees," DAPD quoted a 48-year-old protester as saying. Another man chained himself to one of the trees in the city park that will be affected by the construction work.
The protests threatening to halt Stuttgart 21 — one of the country's major infrastructure projects — have grown into a national issue.
Chancellor Angela Merkel threw her weight behind the project Tuesday, saying its completion is a question of credibility for Germany as a whole.
The issue is overshadowing the upcoming election campaign in Baden-Wuerttemberg state, the area around Stuttgart. Latest polls indicated Merkel's conservative party could loose its majority in the state for the first time in decades.