An Italian thief thanked police for arresting him, saving him from tourists he had just robbed in Rome.

"I must thank you, they were massacring me," the 48-year-old criminal told police after he was arrested near the Theatre of Marcellus, one of the monuments in Rome's historic centre.

The thief, from the northern region of Liguria, stole a handbag from a Korean family when they were not paying attention. He threatened the family with a knife when he was spotted and then tried to flee.

Two men from the family, in their twenties, chased him for several hundred metres before they got him down with taekwondo moves. They disarmed the thief and continued to beat him.

A patrolling police officer intervened, separated the three and arrested the thief immediately.

"Normally tourists will just call us and report the incidents," the officer said. "In this case, the two got really excited and could have seriously injured the thief."

The young Koreans left after they got the handbag back. The thief was transferred to a prison in Rome and will face robbery charges.

Armed robbery in Rome experienced a sharp decline last year with 4,246 cases reported in 2008 compared with 5,133 in 2007.