This photo captured from the website of North Korea's official Korean Central News Agency shows the North's newly built "tactical nuclear attack submarine", Sept. 6, 2023. Yonhap

The military has detected apparent signs that North Korea has started to build a possible nuclear-powered submarine, a lawmaker said Tuesday, amid concerns over Pyongyang's push to acquire advanced weapons.

In January, North Korean leader Kim Jong-un inspected a project to build a nuclear-powered submarine after vowing to develop such a submarine among other sophisticated weapons systems during a ruling party congress in 2021.

"Partial signs that appear to be the start of the submarine's construction have been detected," the Defense Intelligence Agency said in a report to Rep. Kang Dae-sik of the ruling People Power Party.

"As construction is still in its early stages, further confirmation is needed on whether it is nuclear powered," it said, without providing details.

A military official said authorities have spotted the North's construction of a submarine bigger than existing vessels in the northeastern Sinpo area, where its submarine-related facilities are located.

"Its exact tonnage and other (details) can be accurately determined once progress is made," the official said.

The military is said to be looking into the possibility of the vessel being nuclear powered due to its size. But the North is assessed to have yet to acquire a nuclear reactor and other key components for such a submarine.

North Korea has recently pushed to acquire advanced naval vessels, unveiling a new "tactical nuclear attack submarine" in September last year.

South Korea's military, however, has said the submarine does not appear to be ready for normal operations.

North Korea operates approximately 70 submarines, including midget submarines, while South Korea's submarine force consists of about 10 vessels, according to the South's Defense White Paper published in 2023. (Yonhap)