North Korea may have launched multiple ballistic missiles early on Wednesday local time, according to Japanese public broadcaster NHK, which landed in the sea.

The broadcaster, citing Japan's Coast Guard, reported that North Korea had launched "what could be two ballistic missiles." This comes after Japan's Prime Minister's office said that North Korea had launched a suspected ballistic missile.

NHK added that "Japanese government sources say the projectiles seem to have fallen into the Sea of Japan, outside of the country's exclusive economic zone."

On Tuesday, a nuclear-capable US Navy ballistic missile submarine made a port call in South Korea on Tuesday. The presence of the Ohio-class ballistic missile submarine in the South Korean port city of Busan was announced by the country's Defense Ministry on Tuesday afternoon.

The arrival of the submarine, and the ensuing suspected launches on Wednesday follow a period of heightened tensions on the peninsula. Last week, North Korea both tested what it said was an advanced long range missile and threatened to shoot down US military reconnaissance aircraft engaging in what it called "hostile espionage" activities near its territory.

Kim Yo Jong, sister of North Korean leader Kim Jong Un and a senior official in her own right, said in a statement Monday the deployment of a US ballistic missile submarine to the peninsula would damage already fractured lines of communication between the two sides.

South Korea and the US also held their inaugural meeting in Seoul on Tuesday of the Nuclear Consultative Group, a joint panel set up by the countries' leaders at a summit in Washington in April.