South Korean President Park Geun-Hye warned Monday that North Korea's recent submarine-launched ballistic missile test posed a "serious challenge" to regional stability and vowed a strong military response to any provocation from Pyongyang.

Pyongyang's state media announced Saturday that a new SLBM had been successfully tested under the personal supervision of North Korean leader Kim Jong-Un, who described it as a "world-level strategic weapon".

U.N. Secretary-General Ban Ki-moon held a brief meeting in Moscow at the weekend with North Korea's parliament president Kim Yong-Nam, a U.N. spokesman said Monday.

Ban attended World War II commemorations in Moscow as did Kim who traveled to Russia after leader Kim Jong-Un cancelled a much-anticipated visit. 

North Korea did not test fire a ballistic missile from a submarine as Pyongyang claimed over the weekend and the country is still a long way from achieving such a capability, U.S. officials said Monday.

The North's state media said on Saturday that a new submarine-launched ballistic missile (SLBM) had been tested but U.S. officials rejected the regime's account.

South Korea on Monday urged North Korea to halt its "worrisome" development of a submarine-launched ballistic missile, and threatened to respond "mercilessly" to any overt provocation from Pyongyang.

The North's state media announced Saturday that a new SLBM had been tested under the personal supervision of North Korean leader Kim Jong-Un, who described it as an "eye-opening success" that provided his military with a "world-level strategic weapon".

South Korea said Sunday its envoy attending Russia's World War II anniversary ceremony briefly met North Korea's ceremonial head of state, a rare high-level encounter between the rival states.

Senior lawmaker Yoon Sang-Hyun, who was representing South Korean President Park Geun-Hye at the Moscow event, met the North's Kim Yong-Nam on Saturday, Seoul's foreign ministry said.

North Korea said Saturday it had successfully test-fired a submarine-launched ballistic missile (SLBM) -- a technology that could eventually offer the nuclear-armed state a survivable second-strike capability.

North Korean leader Kim Jong-Un, who personally oversaw the test, hailed the newly developed missile as a "world-level strategic weapon", according to a report by the official KCNA news agency.

North Korea on Friday slammed U.S. allegations that its space research is essentially a disguised ballistic missile program, and vowed to send more satellites into orbit in defiance of U.N. sanctions.

Dismissing the "litany of rubbish" put out by the U.S. "barking dogs," the North's National Aerospace Development Administration (NADA) said it would push forward with a robust space launch agenda.

North Korea warned Friday that it was prepared to fire on sight without warning at South Korean naval vessels it accused of violating their disputed Yellow Sea border.

The Korean People's Army (KPA) said 17 South Korean high-speed patrol boats had crossed into the North's territorial waters in the first week of May "under the pretext" of intercepting Chinese fishing boats.

Japan launched a major push at the United Nations on Tuesday to rally support for its drive to settle lingering questions over the decades-old abductions of Japanese nationals by North Korea.

Japan's minister responsible for the abductions issue, Eriko Yamatani, said she is seeking "specific actions" from countries to turn up the pressure on North Korea and to seek information on the fate of the abductees.

A South Korean student held in North Korea for illegal entry has told CNN in an interview from Pyongyang that he wanted to be arrested.

Joo Won-Moon, 21, who attends New York University and has permanent U.S. residency, said he had hoped to create an "event" that could improve relations between North and South Korea.