Three foreigners were indicted Thursday on charges of illegally entering South Korea through the country's main airport last month, prosecutors said Thursday.

The Incheon District Prosecutors' Office, located in the western port city of the same name, said it charged the suspects -- a Chinese couple and a Vietnamese national -- for violating the country's immigration control law.

Two Chinese nationals allegedly sneaked in through Incheon International Airport without being noticed by immigration officials or picked up by the airport's security control system on Jan. 21, prosecutors said.

They were apprehended by the immigration authorities in Cheonan, about 90 kilometers south of Seoul, hours after the Incheon airport announced that the two had broken through security systems and fled the airport.

Meanwhile, the 24-year-old Vietnamese man is accused of forcing his way through the gate of an unmanned automatic immigration checkpoint at Incheon airport on Jan. 29, prosecutors said.

The two cases have prompted public concern over security breaches at the country's main gateway, prompting a state audit agency to hold a massive inspection.

"An investigation shows that the two cases occurred accidentally and were not a premeditated illegal entry," said an Incheon prosecutor, requesting customary anonymity.

The prosecution office said it also indicted a 47-year-old Chinese and a 32-year-old Vietnamese on charges of helping the couple and the man, respectively.

The Chinese suspect allegedly helped the couple find a house to hide in and a new cellphone, prosecutors said.

Following the two high-profile cases, President Park Geun-hye instructed Cabinet officials to strengthen security at the airport.

Soon, the country's airport authority set up a team meant to prevent illegal entry by foreigners. (Yonhap)