Two youths, one armed with an unspecified edged weapon, stole a bag from an employee at a restaurant, and soon after assaulted a security guard, NT Police said.

Police director of communications Mark Wilton said in a statement that about 4:40pm on Tuesday two male youths whose ages were not given, one armed with an unspecified edged weapon, allegedly stole a bag from an employee at a restaurant in the Vic Arcade, in the Smith St mall in Darwin.

He said that a short time later the boys allegedly threatened a security guard at a Cavenagh Street cafe, and then assaulted the guard after the guard confronted them when they attempted to steal from the cafe.

Mr Wilton did not say if the guard was attacked with the weapon, or suffered any injuries, and there was no description of the boys but police said Strike Force Trident detectives were investigating.

Police are asking any witnesses to call them on 131 444, or make an anonymous report through Crime Stoppers on 1800 333 000.