The decision was made during the third day of North Korea’s ruling Workers’ Party of Korea (WPK) congress on Sunday.

Addressing thousands of delegates attending the meeting in the capital, Pyongyang, North Korean Leader Kim Jong-un urged all the participants to press ahead with the “byungjin” policy of twin economic and nuclear development.

“We will consistently take hold on the strategic line of simultaneously pushing forward the economic construction and the building of nuclear force and boost self-defensive nuclear force both in quality and quantity as long as the imperialists persist in their nuclear threat and arbitrary practices,” Kim said, in an apparent reference to the United States and its allies.

The congress endorsed Kim’s “byungjin,” as well as his strategy of using nukes only if the country’s sovereignty is threatened by a nuclear power.

The congress, which opened on Friday, stressed that the nuclear weapons program will move forward as long as there are nuclear threats against the country.

North Korea accuses the US of plotting with its regional allies to topple the government in Pyongyang. The country describes its nuclear capabilities as a deterrent against hostile US policies.

The 7th party congress is the first of its kind in 36 years and also the first during Kim’s, who came to power in late 2011 following the sudden death of his father Kim Jong-il.

Pyongyang declared itself a nuclear power in 2005 and carried out four nuclear weapons tests — in 2006, 2009, 2013 and 2016.

South Korea, the North’s immediate neighbor and traditional adversary, is concerned about the nuclear and missile activities of Pyongyang.

Relations between North and South Korea have been turbulent for years. Seoul and Pyongyang fought a war in the early 1950s, and have been at odds ever since.

Tensions have escalated further recently over joint military exercises by Washington and Seoul.