Berlin police announced Tuesday they had found three improvised pipe bombs near a huge May 1 protest march in what a prominent German lawmaker called an act of terrorism.

The aluminum pipe devices — about 40 centimeters (16 inches) each — were filled with an explosive but were not detonated, police spokesman Stefan Redlich said. If any had exploded, they could have caused serious or deadly injuries up to 15 meters (50 feet) away, he added.

Experts are still investigating the explosive substance and do not yet know whether it could have burst the pipes into pieces, creating a shrapnel bomb, Redlich added.

The bombs were found on sidewalks in Berlin's western Kreuzberg neighborhood as 10,000 leftists rallied on May Day, but police officers thought they were just large fireworks and picked them up to check them later.

The substance in the pipes was made of chlorate and sugar, but experts have not determined how powerful the explosive mixture was, Redlich said.

Police had no immediate information on who might have left the bombs or what their motive may have been. Redlich said no hypothesis could be ruled out — it might have been a leftist attempt to attack police security or an attack targeting the leftist protesters.

The head of Parliament's top security committee, Wolfgang Bosbach, told daily Berliner Morgenpost that the incident has to be taken very seriously "because the perpetrators still live among us and there's no guarantee they will limit their actions to May 1."

Berlin traditionally sees huge leftist protest rallies on May Day and clashes with police are frequent. But over the past years, violence has decreased as the number of police has risen — up to 7,000 this year.

A total of 123 demonstrators were arrested and 124 officers injured during this year's protests.

Police Union GdP's Berlin chief, Klaus Eisenreich, told RBB-Inforadio the bombs represent a new dimension.

"We think they weren't only targeting police officers. This is terrorism," he was quoted as saying.

Germany's Federal Prosecutors' Office — responsible for all major terrorism investigations — said Tuesday its experts will decide whether the case is serious enough for them to take it over from local prosecutors.