SEOUL, South Korea -- In an surprise move that could help ease tensions on the Korean Peninsula, North Korea said Thursday that it would release six South Koreans it has been holding in detention, according to South Korean officials.
The Red Cross of North Korea told its South Korean counterpart that the six would be returned to the South today at the border village of Panmunjom, the South Korean Unification Ministry said in a statement.
It was unclear who the detainees were. The ministry said they were South Korean men ages 27 to 67, but that it was unclear how long they had been in the North, or how they had gotten there.
Pyongyang said in February 2010 that it was holding four South Koreans for illegal entry, but it never responded to Seoul's request that they be identified and released. Last June, the North said it was holding "several" South Koreans for illegally entering the country, but did not elaborate.
Thousands of South Koreans, most of them fishermen, are said to have been taken to the North in the decades since the Korean War; more than 500 of them have not returned, though Pyongyang denies holding them against their will.
South Korea welcomed the announcement Thursday. "Although it is belated, we consider it a good thing that the North has decided to take this humanitarian measure," the Unification Ministry's statement said. "We will get custody of our six citizens, verify their identities and find out how and why they entered the North."
In recent weeks, North Korea has alternated between harsh rhetoric and conciliatory gestures. In mid-September, streams of South Korean vehicles began crossing into the North again, as operations resumed at a jointly run industrial park in the North Korean border town of Kaesong. The complex had been idle since April, when the North withdrew all of its workers amid tensions sparked by its most recent nuclear test.
But soon after the Kaesong complex reopened, North Korea unilaterally postponed resumption of an emotionally charged humanitarian program under which members of families divided by the Korean War have been allowed to hold reunions. The North blamed the postponement on what it called the "reckless and vicious confrontational racket" of the conservative government of South Korean President Park Geun-hye.
Early this month, North Korea lashed out again, advising Ms. Park to "watch her mouth" and threatening to "rain fire" on the South, after South Korean leaders said the North's policy of maintaining its nuclear arms program while rebuilding its economy would never work. Also this month, the North put its military on high alert, warning the United States of "disastrous consequences" for moving warships, including an aircraft carrier, into a South Korean port for a military exercise.
Meanwhile, a Washington-based research institute reported Thursday that the North has increased activity at its main underground nuclear test site, digging new tunnel entrances in what could be preparations for another nuclear test. The U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies in Washington, basing its conclusion on analysis of commercial satellite images of the Punggye-ri site in northeastern North Korea, said there was no sign that a test was imminent.
The report came a day after the North's Foreign Ministry reaffirmed that it would continue to expand its nuclear arsenal, despite U.S. warnings that it will not engage in dialogue Pyongyang is seeking until the North moves toward denuclearization.
North Korea is believed to have recently restarted a reactor at its main nuclear complex in Yongbyon, north of Pyongyang, which would revive its main source of nuclear weapons fuel, plutonium. The North is also believed to be expanding its uranium enrichment capabilities, which would provide it with an alternative nuclear arms fuel source.
But North Korea has also sent less hostile signals recently. On Thursday, South Korean officials said Pyongyang had agreed to allow 24 South Korean lawmakers and their aides to visit the Kaesong complex next Wednesday. The lawmakers will meet with South Korean factory managers there, but will not hold talks with North Korean officials, the officials said.
North Korea is eager to expand the Kaesong complex, where its low-paid workers make textiles, shoes and other labor-intensive goods in South Korean-owned factories. The North's leader, Kim Jong Un, has vowed to attract more foreign investment and improve his people's living standards.
But the South has remained skeptical of expanding the Kaesong project until the two Koreas can agree on measures to prevent another politically motivated shutdown, such as allowing non-Korean investment in the complex. But those negotiations have advanced fitfully; a briefing for potential investors from other nations was canceled this month, with continuing inter-Korean tensions cited as the reason.