Swiss authorities have charged four Iraqi men with planning attacks and helping Islamic State smuggle followers into Europe, Switzerland's attorney general said.

One man, described as a member of a forerunner of Islamic State (IS), entered Switzerland at the start of 2012, and "forged plans for attacks," Switzerland's Office of the Attorney General said in a statement.

"The three accused individuals also aided and abetted smuggling further IS followers to Europe, assumed coordination tasks, disseminated propaganda for the actions of the terrorist organization, gave instructions and also provided operative advice, amongst other things," the offical added.

The individuals, aged 29 to 34, were not named.

All face charges of participating or supporting a criminal organization and preparing an attack as well as entering and exiting Switzerland illegally.