Two South Koreans detained in North Korea told CNN on Sunday that they spied for South Korea.

South Korea has flatly rejected the accusations and urged Pyongyang to release them.

The interviews came after North Korea announced on Saturday that it arrested a South Korean student studying in the U.S. on charges of illegal entry into the country, the fourth South Korean citizen detained in the North.

South Korean missionary Kim Jung-wook has been held there since October 2013.

Sunday's interviews as well as the new detention could be an attempt by Pyongyang to pressure South Korea to shift its policy toward the communist nation. The North could also use the detainees as a negotiating chip should inter-Korean talks reopen.

When announcing last month the arrest of the two CNN interviewees -- Kim Kuk-gi and Choe Chun-gil -- North Korea accused them of working as spies for South Korea's main intelligence agency National Intelligence Service (NIS), branding them "heinous terrorists."

In Sunday's interviews, both Kim, 61, and Choe, 56, admitted to the charges against them and said they would accept any punishment the North Korean government decided. North Korean minders were present during the interviews, CNN said.

CNN also said North Korea is often accused of pushing detainees to make false confessions.

Kim was quoted as telling CNN that he was a missionary struggling financially in northern China when the South's spy agency recruited him. They offered to pay for information about the North, such as itineraries of visits by leaders to foreign countries and copies of new North Korean currency to be used in forgery.

Kim was also quoted as saying he was paid about $500,000 over roughly nine years.

Choe said he was working as a businessman in northern China when he was approached by the South's spy agency to gather information and materials from North Korea. He said he worked as a spy for three years before he was arrested.

They said they were being treated well by the North Koreans, accusing the South of disowning them.

Choe apologized to his family for getting into trouble. Kim said he had no family, but warned other South Koreans against doing as he had done. Kim also praised North Korean leader Kim Jong-un in "glowing terms," according to CNN. (Yonhap)