North Korea will pursue its nuclear and ballistic missile program in defiance of the United States and its allies, a top Pyongyang envoy said Friday, adding that a state of "semi-war" exists on the divided Korean peninsula.

So Se Pyong, North Korea's ambassador to the United Nations in Geneva, denounced the huge joint U.S.-South Korean military exercises taking place that he said are aimed at "decapitation of the supreme leadership of the [Democratic People's Republic of Korea]" and conquering Pyongyang.

North Korea conducted a fourth nuclear test in January and launched a long-range rocket in February. The South Korean military said Friday that North Korea had fired a missile into the sea off its east coast.

"If the United States continues, then we have to make the countermeasures also. So we have to develop, and we have to make more deterrence, nuclear deterrence," So, who is also North Korea's envoy to the U.N.-sponsored Conference on Disarmament, said in an interview with Reuters conducted in English.

"Simultaneous policy is the policy of my country, and my party also, meaning nuclear production and economic development," he said, referring to the twin aims of the policy course of North Korean leader Kim Jong Un that is expected to be endorsed at a congress of the ruling Workers' Party in May, the first in 36 years.

So had no information about the latest missile firing or about South Korean allegations that his country was disrupting GPS signal reception, which Seoul says has forced some boats to return to port amid heightened tensions.

"[Seoul is] making too many manipulations, too many false reports," he said.

U.S. President Barack Obama joined South Korean President Park Geun-hye and Japanese Prime Minister Shinzo Abe on Thursday in vowing to ramp up pressure on North Korea in response to its nuclear and missile tests. The three leaders recommitted their countries to one another's defense and warned they could take further steps to counter threats from Pyongyang.

"Actually that summit, we call it ... a kind of propaganda," So said, dismissing the talks on securing vulnerable atomic materials to prevent nuclear terrorism.

'We Are Going On Our Own Way'

Chinese President Xi Jinping on Thursday also called for dialogue to resolve the "predicament" on the Korean Peninsula during a meeting with Park in Washington, Xinhua news agency said Friday.

Asked whether his reclusive country felt pressure from its ally China and other powers, So replied: "Whether they are going to do anything, we don't care. We are going on our own way.

"[We are] not having dialogue and discussions on that."

The Security Council unanimously passed a resolution in early March expanding U.N. sanctions aimed at starving North Korea of funds for its nuclear and ballistic missile programs.

"We are going against that resolution also because that is not fair and [not just]. At this point, because this is really the war now ... We are busy to deal with this semi-war status of the situation on the peninsula now."

Regarding the joint military exercises being conducted by U.S. and South Korean forces, he said that 300,000 troops are taking part: "Now they [show] their true color, meaning the decapitation of the supreme leadership of DPRK."

Asked about prospects for resuming stalled six-party talks on his country's nuclear program, So replied that denuclearization of the peninsula is no longer on the table.

"If the United States stops their hostile policy towards the DPRK and comes to the peace treaty, then something [might be] different," he said.