The National Office of Investigation said Sunday it will conduct a special crackdown on organized crime for four months, starting from Monday.

A total of 320 dedicated investigation teams of 1,539 police officers will be set up at city and provincial police agencies and police stations across the country to respond with all-out efforts.

Crackdown targets include gangsters involved in gambling websites, fraudulent phone calls and text messages and violations of public welfare by extorting money from people and the obstruction of business at construction sites.

In particular, police recently arrested three alleged gangsters for extorting money from construction companies by threatening to obstruct work by posing as construction union members, through a special crackdown on violence at the sites. Police said they will strongly investigate similar methods during the special crackdown period.

From the early stage of the investigations, police will focus on confiscating money earned via illegal means, to prevent the funding of the criminal organizations.

Meanwhile, among the gangsters nabbed by police last year, those in their 20s and 30s accounted for nearly 60 percent, and the number of gangsters under 20 more than doubled from the previous year, according to statistics from the National Police Agency on Sunday. New inflows and generational replacement have apparently emerged in the world of organized crime.

Of the 3,231 people arrested for organized crime last year, 244 were caught entering the gang world, up 20.1 percent from the previous year, the National Police Agency said Sunday.

Dividing those arrested by age, 1,030 were in their 20s, accounting for 31.9 percent, and 877, or 27.1 percent, were in their 30s. There were 210 arrests of those under 20, an increase by 114.3 percent from the previous year.

An official from the National Police Agency said, "We will curb the expansion of the power of existing gangs and investigate new organizations more strictly."