SEOUL, SOUTH KOREA - North Korea said Friday its two latest rounds of weapons tests this week were successful while vowing to bolster its nuclear "war deterrent" and speed up the development of more powerful warheads.

It appeared North Korean leader Kim Jong Un did not attend the tests Tuesday and Thursday, which were detected by the militaries of neighbors South Korea and Japan. But Kim did inspect a munitions factory where workers pledged loyalty to their leader, who "smashes with his bold pluck the challenges of U.S. imperialists and their vassal forces," state media said.

North Korea has been ramping up its testing activity in recent months, including six rounds of weapons launches so far in 2022, demonstrating its military might amid pandemic-related difficulties and a prolonged freeze in nuclear diplomacy with the United States.

While aggressively expanding his military capabilities despite limited resources, Kim is also reviving Pyongyang's old playbook of brinkmanship to wrest concessions from Washington, which leads international sanctions over the North's nuclear program.

The North's official Korean Central News Agency described the two ballistic missiles launched from a coastal area on Thursday as "surface-to-surface tactical guided missile" armed with a conventional warhead and said they accurately struck a sea target.

Photos released by state media suggest the weapons test-fired were a short-range solid-fuel missile it apparently designed after Russia's Iskander ballistic system.

The missile, which North Korea has tested since 2019, could be launched from launcher trucks and trains and is designed for maneuverability and low-altitude flight. It's seen as a key piece in the country's expanding arsenal of shorter-range weapons apparently aimed at overwhelming missile defenses in the region.

KCNA said Tuesday's launches were of a purported long-range cruise missile the North first tested in September. The two missiles flew for more than 2 hours and 35 minutes and demonstrated an ability to strike targets 1,800 kilometers away, a performance that underscored their value in "boosting the war deterrence of the country," the agency said.

People watch a TV showing a file image of North Korea's missile launch during a news program at the Seoul Railway Station in Seoul, South Korea, Jan. 25, 2022.

The North has described this weapon as "strategic," implying that it's being developed to deliver nuclear weapons.

Kim had attended a Jan. 11 test-firing of a purported hypersonic missile he described as the most significant part of a five-year plan to build up the North's military force. His wish list also includes multi-warhead missiles, spy satellites, solid-fuel long-range missiles and submarine-launched nuclear missiles.

KCNA, in its separate report on Kim's visit to a munitions factory, said the facility was producing a "major weapon system." It didn't say when he visited.

Touring the facility with top officials, including his increasingly powerful sister Kim Yo Jong, Kim Jong Un "highly appreciated" the workers' efforts to modernize the country's military and their devotion to defend the ruling Workers' Party's revolutionary cause with "powerful cutting-edge arms," the KCNA said.

North Korea has described its weapons tests as a rightful exercise of self-defense and threatened stronger action after the Biden administration imposed fresh sanctions following this month's hypersonic tests.

In a ruling party meeting chaired by Kim last week, senior party members made a veiled threat to resume testing of nuclear explosives and long-range missiles targeting the American homeland, which Kim suspended in 2018 while initiating diplomacy with the United States.

Kim's summitry with then-President Donald Trump derailed in 2019 after the Americans rejected North Korea's demands for major sanctions relief in exchange for a partial surrender of its nuclear capabilities.

Cha Deok-cheol, spokesperson of South Korea's Unification Ministry, which handles inter-Korean affairs, said during a briefing that the North's missile tests "turn the Korean Peninsula's clock back to the times of tensions and conflict" and the North should halt the launches and return to dialogue.

Some experts say North Korea could dramatically escalate weapons demonstrations after the Winter Olympics, which begin Feb. 4 in China, the North's main ally and economic lifeline.

They say Pyongyang's leadership likely feels it could use a dramatic provocation to move the needle with the Biden administration, which has been preoccupied with bigger adversaries including China and Russia. The Biden administration has offered open-ended talks but showed no willingness to ease sanctions unless Kim takes real steps to abandon the nuclear weapons and missiles.