The announcement came ahead of a new round of nuclear negotiations between Pyongyang, Seoul and Washington, but there was no clear indication in the North's announcement if it would be willing to deal away its arsenal.
The North rather expressed confidence about its nuclear force, which leader Kim Jong Un declared as complete in November after a slew of weapons tests that included the underground detonation of a purported thermonuclear warhead and flight tests of three intercontinental ballistic missiles.
Some analysts believe Kim is entering the negotiations from a position of strength and is unlikely to accept a significant cut of his arsenal. South Korean and US officials have said Kim is likely trying to save his broken economy from heavy sanctions,
After the announcement Saturday about testing, US President Donald Trump tweeted, "This is very good news for North Korea and the World" and "big progress!"
He also said he's looking forward to his upcoming summit with Kim.
The North's official Korean Central News Agency said the country is making the move to shift its national focus and improve its economy.
The North also vowed to actively engage with regional neighbors and the international community to secure peace in the Korean Peninsula and create an "optimal international environment" to build its economy.
The announcements came days before Kim is set to meet South Korean President Moon Jae-in in a border truce village for a rare summit aimed at resolving the nuclear standoff with Pyongyang.
A separate meeting between Kim and Trump is anticipated in May or June.
The North's decisions were made in a meeting of the ruling party's full Central Committee which had convened to discuss a "new stage" of policies.
The Korean Workers' Party's Central Committee declared it a "great victory" in the country's official "byungjin" policy line of simultaneously pursuing economic and nuclear development.
The committee unanimously adopted a resolution that called for concentrating national efforts to achieve a strong socialist economy and "groundbreaking improvements in people's lives."
"To secure transparency on the suspension of nuclear tests, we will close the republic's northern nuclear test site," the party's resolution said.
The agency quoted Kim as saying during the meeting: "Nuclear development has proceeded scientifically and in due order and the development of the delivery strike means also proceeded scientifically and verified the completion of nuclear weapons.
"We no longer need any nuclear test or test launches of intermediate and intercontinental range ballistic missiles and because of this the northern nuclear test site has finished its mission."
Seoul says Kim has expressed genuine interest in dealing away his nuclear weapons. But North Korea for decades has been pushing a concept of "denuclearization" that bears no resemblance to the American definition, vowing to pursue nuclear development unless Washington removes its troops from the peninsula.