ATHENS  A powerful car bomb rocked the Athens Stock Exchange on Wednesday, badly damaging parts of the building, setting eight vehicles ablaze and slightly wounding a private security guard, the police said.

The blast came 40 minutes after a smaller bomb exploded outside a government building in Thessaloniki, northern Greece, causing minor damage but no injuries.

Both attacks Wednesday were preceded by warning calls made by anonymous callers. Officials said they did not believe the two were linked.

Image A view of the damaged stock exchange in Athens on Wednesday morning. Credit... Louisa Gouliamaki/Agence France-Presse — Getty Images

There was no immediate claim of responsibility for either, but police and counterterrorism officials said they suspected the Athens blast was set off by Revolutionary Struggle, a far-left militant group that fired a rocket at the United States Embassy here two years ago.