Yonhap reported that the DPRK launched at least one ballistic missile into the sea hours after a senior US official confirmed on Tuesday that a US nuclear-armed ballistic missile submarine (SSBN) is in South Korea, in a first since the 1980s.

The launch was confirmed by South Korea's Joint Chiefs of Staff, who claimed they were still determining what sort of missile had been fired and that it had fallen in the East Sea, commonly known as the Sea of Japan.

According to the Kyodo news, Japan's Coast Guard believes a second missile was launched.

The DPRK also fired a ballistic missile on Wednesday according to Seoul's military, two days after US spy planes violated its airspace.

Last week, state media of the DPRK reported that it successfully conducted a missile test of the ICBM solid-fuel Hwasong-18.  

On Monday, the DPRK accused a US spy plane of violating the DPRK's airspace and continued to decry US plans to deploy a nuclear missile submarine near the Korean peninsula.

A spokesperson for the DPRK Ministry of National Defense said in a statement that the US had "intensified espionage activities beyond the wartime level," citing "provocative" spy plane flights over a period of eight consecutive days this month.

"There is no guarantee that such a shocking accident as the downing of the US Air Force strategic reconnaissance plane will not happen in the East Sea of Korea," the spokesperson added.

Kim Yo Jong, the Deputy Department Director of the Publicity and Information Department of the Workers' Party of Korea, warned the United States on Monday against any "foolish act" that would jeopardize its security and dismissed offers of negotiations as a ruse, according to state news agency KCNA.

Kim's remarks came after the White House expressed its concern that the country might conduct another intercontinental ballistic missile (ICBM) test after it fired an ICBM off its east coast last week.