Russian authorities say at least 78 people have become ill after an unidentified gas was released in a store in the northwestern city of St. Petersburg.

A spokesman for the Emergency Situations Ministry says containers, equipped with timing mechanisms, were found in three shops belonging to the Maxidom hardware chain.

The gas was released in at least one of the stores. None of the victims appeared to be critically ill, but more than 50 sought medical attention or were hospitalized.

Local media quote authorities as saying the attack was probably carried out by criminals.

Some information for this report provided by AFP and Reuters.