SEOUL, South Korea (AP) — South Korea placed overseas travel bans on three people as part of an investigation into alleged drone flights over North Korea that have deepened animosities between the rivals, authorities said Friday.

North Korea threatened retaliation earlier this month after accusing South Korea of launching a surveillance drone flight in September and again in January. The South Korean government denied operating any drones during the times specified by North Korea and began probing if civilians sent them.

The development threatens to further dampen prospects for a push by South Korea’s liberal government to resume long-stalled talks with North Korea.

The three civilians put under travel bans include a man with the surname Oh who told South Korean media that he flew drones to check radiation levels at a North Korean uranium facility, according to a joint military and police investigation team.

The investigation team refused to give details about two other civilians except to say one was summoned for questioning in the past week.

South Korea media reported the trio has worked together for a drone manufacturer and that Oh and the person who was summoned worked as contract employees for the office of then conservative President Yoon Suk Yeol in 2022. The investigation team declined to confirm the reports.

President Lee Jae Myung has called for a thorough probe, saying unnecessary tensions with North Korea would cause negative impacts on the economy. Lee took office last June via a snap election arranged after the early departure of Yoon, who was dismissed as president over his ill-fated martial law imposition in late 2024.

Analysts say North Korea’s drone accusations were likely driven by its efforts to dial up anti-South Korea sentiments ahead of the ruling Workers’ Party congress expected in late January or February. North Korea could add leader Kim Jong Un’s declaration of a hostile “two-state” system on the Korean Peninsula in the party constitution during the congress, the first of its kind in five years.

There have been no public talks between the two Koreas since 2019 and drone flights are a source of animosity between the rivals.

North Korea accused South Korea in October 2024 of flying drones over its capital, Pyongyang, to drop propaganda leaflets. South Korea has accused North Korea of occasional drone flights over the border in the past decade.

In December 2022, South Korea fired warning shots, scrambled fighter jets and flew surveillance drones over North Korea in response to North Korea’s first alleged drone flights across the border in five years.