WARSAW, Poland (AP) — Police in Warsaw said Monday they have detained a 31-year-old man who placed an explosive device in a downtown street where over 300 people were gathering.

The police said on Twitter they have evacuated the area in 200-meter (yard) radius and experts have come with specialized equipment to remove the explosive device. Warsaw police spokesman Sylwester Marczak said it's a powerful device and described the situation as “serious.”

There were no reports of any explosions or anyone being hurt in the incident, which took place a few blocks from the country's presidential palace.