North Korea said Wednesday it successfully tested a new hypersonic missile it implied was being developed as nuclear capable, as it continues to expand its military capabilities and pressure Washington and Seoul over long-stalled negotiations over its nuclear weapons.

The missile test early Tuesday was North Korea's third round of launches this month and took place shortly before North Korea’s U.N. envoy accused the United States of hostility and demanded the Biden administration permanently end joint military exercises with South Korea and the deployment of strategic assets in the region.

A photo published in North Korea's state media showed a missile mounted with a finned, cone-shaped payload soaring into the air amid bright orange flames. The official Korean Central News Agency said the missile during its first flight test met key technical requirements, including launch stability and the maneuverability and flight characteristics of the “detached hypersonic gliding warhead.”

Read:North Korea fires suspected ballistic missile into sea

The North’s announcement came a day after the South Korean and Japanese militaries said they detected North Korea firing a missile into its eastern sea. The U.S. Indo-Pacific Command said the launch highlighted “the destabilizing impact of (North Korea’s) illicit weapons program.”

North Korea last week made offers to improve relations with the South if certain conditions are met, apparently returning to its pattern of mixing weapons demonstrations with peace overtures to wrest outside concessions.

Negotiations over its nuclear program have been in a stalemate since February 2019. North Korea has demanded the lifting of U.S.-led sanctions while insisting it has the right to a nuclear weapons program. U.S. officials have made it clear the sanctions will stay in place until the North takes concrete steps toward denuclearization.

North Korean leader Kim Jong Un in recent political speeches has vowed to bolster his nuclear deterrent in the face of U.S. pressure. His government has so far rejected the Biden administration’s offer to resume talks without preconditions, saying that Washington must abandon its “hostile policy” first, a term North Korea mainly uses to refer to sanctions and joint U.S.-South Korea military drills the North considers to be an invasion rehearsal.

In a separate report, KCNA said the North’s rubber-stamp parliament opened a session on Tuesday and discussed domestic issues such as economic policies and youth education and that the meetings would continue. Some experts speculate the North might use the session to address the deadlock on nuclear diplomacy, but the state media report did not mention any comments made toward Washington and Seoul.

Read:Seoul: North Korea fires 2 ballistic missiles off east coast

At a ruling party meeting in January, Kim named hypersonic glide vehicles, which are launched from a rocket before gliding into a target, among a wish-list of sophisticated military assets. KCNA described the new missile as an important addition to the country’s “strategic” weaponry, implying that the system is being developed to deliver nuclear weapons.

The report also said the test confirmed the stability of the missile’s fuel capsule, indicating a technology to add liquid propellant beforehand and keep it launch-ready for years. And a North Korean official said the North planned to expand the system to all its liquid-fuel missiles.

Liquid-fuel missiles are more vulnerable than solid-fuel missiles because they need to be fueled separately and transported to launch sites using trucks that can be seen by enemy satellites or other military assets.

Kim Dong-yub, a professor at the University of North Korean Studies in Seoul, said North Korea is trying to improve the mobility of these weapons.

Last week, the influential sister of Kim Jong Un reached out to Seoul twice, saying her country was open to resuming talks and reconciliatory steps if conditions are met.

Read: North Korea says it tested new long-range cruise missiles

Analysts say North Korea is using the South’s desire for inter-Korean engagement to pressure Seoul to extract concessions from Washington on Kim's behalf as he renews an attempt to leverage his nuclear weapons for badly needed economic and security benefits.

North Korea’s weapons displays could also be aimed at shoring up domestic unity as Kim Jong Un faces perhaps his toughest moment nearing a decade in rule, with pandemic border closures unleashing further shock on an economy battered by sanctions and decades of mismanagement.

Experts say the North will likely continue its testing activity in the coming months as it dials up its pressure campaign, at least until China begins pushing for calm ahead of the Beijing Olympics early next year.