N. Korea ready to conduct nuke test 'at any time': Seoul's defense minister

Lee made the remarks in a briefing to the National Assembly's defence committee, amid tensions heightened by the North's provocative acts, such as its recent unveiling of the Hwasan-31 tactical nuclear warhead and the test of an underwater nuclear attack drone.

"(North Korea) has already completed preparations for what would be its seventh nuclear test, and is capable of carrying out a nuclear test at any time," Lee told lawmakers.

In a report to the committee, his ministry said the North's nuclear test, if pressed ahead, might be designed for "final technological verification" needed for the mass production and operational deployment of nuclear warheads, reported Yonhap.

It also said the South and the United States have crafted joint military measures to respond to a possible North Korean nuclear test with an aim to demonstrate their alliance's "strong" will.

The measures include the allies' combined show of force, involving America's strategic military assets. It did not elaborate further.

The South Korean military has been strengthening its monitoring of the North's Punggye-ri nuclear test site, it added.

Views on the timing of the North's nuclear test have varied.

Some said the North may not conduct a test anytime soon, given that it appears to have acquired enough technologies through six nuclear tests, including the last in 2017, with leader Kim Jong-un calling for an "exponential" increase in the country's nuclear arsenal. Others said the regime might see a technological imperative to refine technologies for tactical and other nuclear arms.

In the briefing, the ministry touched on the North's steady push to acquire various nuclear delivery vehicles, noting the regime has used recent South Korea-US military drills as a pretext to test and confirm the capabilities of those vehicles.

The delivery vehicles include submarine-launched ballistic and cruise missiles, underwater attack drones and an assortment of missiles using varied launch platforms, such as trains, silos and transporter erector launchers.

Asked if the South has any measure to counter threats from the North's underwater nuclear attack drones, Lee said it "basically" has the capability to detect underwater infiltration vehicles.