STOCKHOLM (Reuters) - Swedish police said they put forces on national alert on Friday after a series of militant attacks in Europe, although the nation's terrorism threat level remained unchanged.
Earlier this week a gunman shot dead four people and injured 22 in a late-night rampage in the centre of Vienna before being killed by police.
France has suffered a number of attacks in recent weeks.
"The aim is, among other things, that the police can react quickly should there be a terror attack," Swedish police said in a statement.
The regional Sydsvenskan newspaper said the police were reacting to a concrete threat against the country. A spokesman for the police declined to give further information.
The heightened security situation could mean a greater police presence in certain places, the statement said, but the public were not told to avoid specific locations.
Swedish police said the threat level against the country remained at 3 on a scale of 5, indicating a heightened risk of attack.
"By declaring a national alert, we get a more flexible organisation which can both prevent an attack taking place and react quickly if an event happens," Head of Operations at the National Operations Department, Stefan Hector, said in the statement.
A national alert allows the police to set up a special task force outside the normal organisational structure, and can be used in cases of national threats, such as terrorism or natural disasters, or local events, such as football matches or state visits.
(Reporting by Simon Johnson; editing by Niklas Pollard, William Maclean)