The incident occurred on Saturday night in Hutwil, a town, police sources said.
The young men, with shaved heads and dressed in military gear, were heard shouting “sieg Heil, sieg Heil” and making Nazi salutes as they marched around the town, according to police and media reports.
One of the men demolished a kebab stand at the restaurant and police were contacted around 8pm about three right-wing extremists ready to attack the owner.
“It must be assumed that according to initial investigations the three men had attacked the Sri Lankan, owner identified as Ibrahim Ekemen, 34
A passerby intervened but the owner was slightly injured, the report said.
The men threatened to kill the restaurant owner “the next time”.The attackers also destroyed a chair and damaged a table, local media reports.
Police identified the men as coming from the cantons of Bern, Fribourg and Zurich.
The regional prosecutor said they were all intoxicated, with one man testing three milligrams per millilitre on a blood alcohol test, six times the legal limit for driving.