Some 20 taxis were called to the official residence of South Korean President Yoon Suk Yeol in the early hours of Monday by an unidentified caller, local police said, as officials are conducting an investigation for possible "obstruction of business."

According to Yongsan Police Station, the score of taxis were stopped by police stationed at Yoon’s residence in Hannam-dong, Yongsan-gu, Seoul, while attempting to enter the premises between 2:30 a.m. and 4:20 a.m. Monday. It was found that the drivers were called there by an unknown person or people.

The drivers told officers that they merely followed the GPS based on the directions given by the caller, which led them to the presidential residence.

Officials are conducting an investigation to find out if the calls were made by a single person or multiple individuals, and to see if they constitute an "interference of business" stipulated by the Article 314 of the Criminal Act. Such a crime would have to involve the circulation of false facts, the threat of force or inputting false information into a data processor, and could be punished by up to five years in prison or a 15 million won ($11,200) fine.

Police have since reinforced security around the presidential residence, officials said.