Fighters for a Free North Korea leader Park Sang-hak in a video the group released on April 30, where he said his group of North Korean defectors flew anti-Pyongyang leaflets to North Korea across the inter-Korean border from areas close to the demilitarized zone in Gyeonggi and Gangwon provinces from April 25 to 29 / Yonhap

Police on Thursday raided the office of a vocal North Korean defector who claimed to have sent anti-Pyongyang propaganda leaflets into the North in defiance of a ban.

Police launched an investigation after Park Sang-hak, head of Fighters for a Free North Korea, a North Korean defectors group, said the organization sent 10 balloons carrying around 500,000 leaflets between April 25-29.

"We are currently searching relevant locations," an official with the Seoul Metropolitan Police said. "We will conduct a swift and strict investigation."

If confirmed, Park's group will be the first to have sent the leaflets critical of the Kim Jong-un regime since Seoul banned such activity under a revised law in March.

Violations of the law are punishable by up to three years in prison or up to 30 million won ($27,000) in fines.

The North Korean regime threatened "corresponding action" in response to the "intolerable provocation." (Yonhap)