Transactions among affiliates of South Korea's large business groups fell in 2020 from a year earlier on tough regulations, the antitrust regulator said Tuesday.

The value of inter-affiliate transactions by 2,182 units of 71 large business groups amounted to 183.5 trillion won ($155 billion) last year, down 13.2 trillion won from 196.7 trillion won the previous year, according to the Fair Trade Commission.

Such deals accounted for 11.4 percent of all business contracts clinched by them last year, down from 12.2 percent a year earlier.

Large business groups with assets exceeding 5 trillion won are required to publicly file their business information, and those with 10 trillion won in assets or more are banned from making equity investments among affiliates or offering loan guarantees to each other.

The number of business groups subject to the commission's tough filing rules rose to 71 for this year from 62 the previous year.

Internal trading has been blamed for allowing owner families to easily net large profits by having subsidiaries award lucrative contracts to each other, undermining the principle of fair competition.

Inter-affiliate transactions by the country's top 10 conglomerates, including Samsung Group and Hyundai Motor, came to 135.4 trillion won last year, down 15 trillion won from a year earlier.

Of the 10 large companies, only two conglomerates -- Samsung and Hyundai Motor -- reported a rise in the value of inter-unit trading.

Hyundai Motor, the country's largest carmaker, clinched the largest deals with its units, valued at 38.5 trillion won, followed by energy and telecom giant SK Group with 30.2 trillion won and Samsung with 26.8 trillion won.

The commission said unlisted firms and conglomerates run by owners reported relatively high portions of inter-affiliate trading. (Yonhap)