North Korean state media said on Friday that Pyongyang has pledged to strengthen its nuclear force "in quality and quantity" and expand the role of its intelligence agency.

At a meeting of the Workers' Party's Central Military Commission on Thursday, North Korean leaders discussed plans to modernize the country's armed forces, with supreme leader Kim Jong Un saying that only a strong military can guarantee "true peace," according to the KCNA news agency.

"The meeting suggested tasks and ways for expanding in a multifaceted manner the functions and missions of the General Bureau of Reconnaissance and Intelligence, which plays a key role in controlling potential threats from enemies and collecting key information, as well as enhancing its capability for military reconnaissance and intelligence activities in a radical manner," KCNA reported.

The commission also presented plans to accelerate the construction of modern naval bases and improve combat systems, according to the agency.

The US Congressional Research Service says Pyongyang has developed its nuclear program over the past decade, posing a growing threat to the US and East Asia.

Pyongyang has conducted six confirmed nuclear weapons tests since 2006.

This comes after a North Korean soldier was reportedly taken into custody in South Korea after crossing the Korean Demilitarized Zone last month.

South Korea's Joint Chiefs of Staff said in a statement that the military had "secured custody of a North Korean soldier on the central front" and that authorities were investigating the details, according to Yonhap news agency.

The demilitarized zone is one of the most secured borders in the world, heavily fortified with barbed wire, landmines and extensive surveillance.

South Korea's Unification Ministry says more than 34,000 North Koreans, including 899 military personnel, have defected to the South since records began in 1998.