Two men dressed as Father Christmas attacked a guard outside Sweden's Royal Palace in Stockholm on Friday and escaped with his loaded gun, police said.

"A little before 2:00am (0100 GMT), the two men, dressed in Father Christmas clothes and masks, entered a restricted area by a guard post, hit him, and then ran off," said Anders Krook, a Swedish police officer.

A second soldier tried to help his comrade and pursued the men, but they escaped in a nearby parked car, Krook told AFP.

The attackers made off with the soldier's loaded AK-5 automatic rifle, a standard-issue weapon in the Swedish army.

"It seems it was organised, given the circumstances," Krook said.

Krook would not comment on how two civilians in fancy dress were able to overpower a guard with a weapon.

The Royal Palace is protected by soldiers, but Sweden's royals live in a castle in the suburb of Drottningsholm.