Madrid (CNN) -- A small device exploded in a Roman Catholic cathedral in the northern Spanish city of Zaragoza Wednesday, but no injuries were reported, a Spanish national police spokeswoman said.
The explosion, thought to be from a camping gas cylinder, occurred shortly before 2 p.m. (8 a.m. ET) in the Basilica of Our Lady of the Pillar, according to the spokeswoman, who by custom is not identified.
The sanctuary was open at the time of the blast, but no one was injured. It was immediately evacuated and cordoned off while police investigate. It was unclear how much, if any, property damage was caused, the spokeswoman said.
The cathedral, whose towering spires dominate the riverfront city of Zaragoza, was built in the 1600s.
It's not clear who planted the device, but Spain's state-run news agency EFE, citing police sources, reported that suspicion falls on small leftist groups who are also thought to be responsible for a small explosive device that police deactivated last February in Madrid's Almudena cathedral. But the police spokeswoman in Madrid would not confirm those details to CNN.
Reports about the explosion first surfaced on Twitter.