Pyongyang, North Korea - North Korea has fired at least two ballistic missiles towards the East Sea, as the Sea of Japan is also known, the South Korean armed forces said on Tuesday.

South Korea's general staff said it detected the launch of two short-range ballistic missiles. It was not initially known how far they flew.

North Korea is prohibited from testing ballistic missiles by UN resolutions. Depending on their design, such missiles can be equipped with a nuclear warhead. North Korea has increased the scope and speed of its missile tests since last year.

The launches came a day after South Korea and the United States kicked off a major joint exercise dubbed Freedom Shield.

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Pyongyang had recently threatened countermeasures should the US and South Korea keep staging military exercises. This was taken to mean a new series of missile tests or a new nuclear test by regional observers.

Washington and Seoul reject Pyongyang's repeated accusations that the maneuvers are part of preparations for an attack.

North Korea said it fired two missiles from a submarine in the East Sea on Sunday. This test is said to have also served as a nuclear deterrent.

Tensions on the Korean peninsula have increased considerably again since last year, with North Korea increasingly testing nuclear-capable missiles.