North Korea launched two short-range ballistic missiles, says South Korea

North Korea has launched two short-range ballistic missiles, which landed in the sea between the Korean Peninsula and Japan, according to South Korea's Joint Chiefs of Staff (JCS).

The missiles were launched from North Korea's Sunan area, JCS said, and were fired in the early morning on Wednesday local time. After flying about 550 kilometers each, the missiles landed in the sea, it added.

"The detailed specifications of these missiles are being analyzed by intelligence authorities of South Korean and the US," JCS said. Japan's Prime Minister's office also tweeted that at least one ballistic missile had been launched.

The launches follow a period of heightened tensions on the peninsula.

On Tuesday, a nuclear-capable US Navy ballistic missile submarine made a port call in South Korea. 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.

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.

The arrival of the submarine comes after North Korea last week 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.

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.

CNN's Brad Lendon and Gawon Bae contributed to this report.