A North Korean soldier looks south on the north side of the truce village of Panmunjom in the demilitarised zone (DMZ) separating the two Koreas in Paju, about 55 km north of Seoul, in this December 6, 2008 file photo.
North Korean security officials have detained two Korean-American journalists who were filming across the Tumen River from the Chinese side of the border, South Korean media and diplomatic sources said on Thursday.
The arrests come at a time of mounting tension on the Korean peninsula, with the North accusing the United States and South Korea of using joint military exercises which end on Friday as preparations to invade the isolated state.
In Washington, a State Department official who spoke on condition that she not be named, said the United States had contacted North Korean authorities about the two, who were detained on Tuesday, and was seeking their immediate release.
"Two American citizens were taken into custody at the Tumen River border between China and North Korea by North Korean border guards," she said. "We have been in touch with North Korean authorities to express our concern about this situation and to secure the immediate release of our citizens."
A diplomatic source said the reporters were on the frozen Tumen river when taken by North Korean security guards. The Tumen runs along the eastern section of the border with China.
The YTN channel earlier quoted a South Korean government official as saying North Korean guards crossed the border into Chinese territory to arrest the two women on Tuesday after they ignored warnings to stop filming.
But the diplomatic source said it was not clear which side of the border they were on at the time.
YTN said the women worked for an online news company based in California but gave no other details. A media source said the two were working for Current TV, a U.S.-based online news company.
Chinese Foreign Ministry spokesman Qin Gang said Beijing was investigating the report and declined to comment further. South Korea's foreign ministry also declined to confirm YTN's report.
YTN said a man was also with the pair from the same news organisation but managed to escape.
"It's difficult to comment on this matter because it involves a U.S. citizen, but our government is aware that a U.S. journalist is in detention in the North," the senior South Korean government official was quoted as saying.
Tensions have escalated on the Korean peninsula in recent weeks.
North Korea has said it will launch a missile early in April as part of its space communications programme, but the United States says the launch is intended to test a rocket that could potentially carry a warhead as far as U.S. territory.
North Korean Premier Kim Yong-il is visiting China, the nearest the impoverished state has to a major ally and a key source of economic aid.
China has avoided openly pressuring the North over its plans to launch the rocket.
In publicly reported comments to Kim, Chinese President Hu Jintao kept to that gentle approach, avoiding direct mention of the rocket issue.
"We hope all sides will take the broader perspective to appropriately resolve existing disputes," Hu told Kim, according to Chinese state radio news.