According to reports in the Korean media, the NTS has indicated that it will bolster its foreign business investigation unit by employing an additional 30 auditors from next month. These auditors will focus on businesses that are wholly foreign owned, or have a foreign shareholding which exceeds 50 percent.

"The nature of business is becoming more global, making it necessary for the government to make changes as well," said Kim Young-geun, an audit planning director at the tax office, according to the Korea Herald.

"The restructuring will allow resources to be focused on areas with greater importance," Kim added.

The international transactions of local companies will also come under greater scrutiny from the tax investigators.

The announcement comes at a time of growing concern by the Korean authorities that foreign entities are deliberately evading taxes by employing shell companies located in offshore jurisdictions.

According to reports last month, an official from the NTS revealed that the tax agency had discovered a number of discrepancies in the income tax declarations of 137 foreign firms made in March.

Among those firms, 70 companies were alleged to have failed to withhold income taxes from employees' wages, while 42 firms supposedly paid no corporate income tax to the Korean authorities on the grounds that they are headquartered offshore. The remaining 25 were said to have been dishonest on their tax declarations.

The official also revealed that the NTS has conducted a transfer pricing review on the May tax payments of the 345 foreign companies operating in Korea whose annual sales are at least 50 billion won ($48.5 million), although the tax department has denied the reports.

In April, it emerged that the NTS had begun investigating a number of foreign investment fund firms, including Newbridge Capital, Carlyle Group, Lone Star Funds and Citigroup and the Government of Singapore Investment Corporation (GIC) for alleged tax evasion relating to the proceeds of property sales.