Police in the Russian city of St Petersburg have found explosives, detonators and a gun in a cinema closed for repairs, Russian media have said.
Interior Ministry officials said that the discovery followed the arrest of three men from Kazakhstan.
The three were arrested by organised crime police, and security sources said they were probably petty criminals.
Russia is on high alert following a wave of terrorist attacks, including last week's school hostage-taking.
At least 326 people were killed when the siege in the North Ossetian town of Beslan ended in bloodshed on Friday.
The discovery of explosives was made at 2000 local time (1600 GMT) on Wednesday in offices in the Progress cinema, gazeta.ru website reported.
Police found 23 cartridges, 900g of plastic explosives, a 200g stick of dynamite, two home-made bombs and a rifle.
A search of the premises is continuing, as police believe there could be another cache.
The cinema is in the same block as a police station and local government offices, gazeta.ru said.
Police say the owners of the explosives were probably using the cinema as a store and were planning to use them somewhere else.
But they are not ruling out the possibility that an attack was being planned in the cinema itself.
Gunmen who seized a Moscow theatre in October 2002 taking hundreds of hostages are thought to have brought weapons into the building in the guise of builders carrying out repairs.
However, Reuters news agency quoted a security source in St Petersburg as saying the explosives there were probably intended for small-time criminal activities.
BBC Russia correspondent Steven Eke says St Petersburg suffers from high levels of crime, including bombings of rival businesses and contract killings.