North Korea has facilities on standby to test a nuclear explosion and could do so at any time, the chief of South Korea's main spy agency said Monday, according to a lawmaker and a government official.

"Facilities for a nuclear test are always on standby and considering the North's capability, the possibility (of a test) is always open," spy agency chief Kim Seung-kyu was quoted as telling a closed meeting of the parliamentary intelligence committee.

However, Kim said there is no sign that a test is imminent, according to two people at the meeting, Rep. Shin Ki-nam, head of the committee, and a government official who requested anonymity, citing policy.

"Currently, however, there is no direct sign or movement that North Korea is preparing a nuclear test," Kim was quoted as saying.

CountryWatch: North Korea

Kim also was quoted as saying his agency detected signs in the late 1990s that the communist nation was digging a tunnel in the northeast and has since kept a close watch on it. Recently, what were believed to be cables were seen in the region, but it's difficult to determine whether they are directly related to a nuclear test, Kim was quoted as saying.

Cables could be used to provide electricity to a tunnel or to link an underground testing site to outside measuring equipment, Shin said.

Concerns of a nuclear test by the Pyongyang flared anew earlier this month after ABC News quoted U.S. officials as saying that suspicious activity was detected at a suspected underground nuclear testing site.

North Korea claims to have nuclear weapons, but has not performed any known test. Many experts believe the North has enough radioactive material to build at least half a dozen nuclear weapons.

On Saturday, the North's Foreign Ministry said it would take "all necessary countermeasures" unless the U.S. accepts its demand for an end to financial restrictions on the country.

The North didn't elaborate what those countermeasures would be, but some local media said the North's statement may mean a nuclear test.

The communist state test-fired seven missiles July 5, including a long-range Taepodong-2 missile, believed potentially capable of reaching the United States.

There have been concerns the North may conduct more tests. But Kim, the South's spy agency chief, said the possibility is low because the North removed all Taepodong-2 related equipment from a launch site on its east coast mid-July, "ending missile activity in the region," according to Shin and the government official.

The United States, China, Japan, Russia and South Korea have tried to persuade the North to abandon its nuclear program at six-party negotiations. The talks have been on hold since November as North Korea refuses to attend until Washington lifts financial restrictions on it.

The nuclear talks have taken on new urgency after the North's missile launches.

The U.S. has urged the North to come to the talks without conditions, saying the financial issue is unrelated to the six-party talks.