SEOUL, South Korea (AFP) — North Korea fired two ballistic missiles Thursday as it claimed its recent blitz of sanctions-busting tests were necessary countermeasures against joint military drills by the United States and South Korea.

As the United Nations Security Council met to discuss Pyongyang's Tuesday launch of an intermediate-range ballistic missile over Japan, North Korea blamed Washington for "escalating the military tensions on the Korean peninsula."

The recent launches — six in less than two weeks — were "the just counteraction measures of the Korean People's Army on South Korea-US joint drills," Pyongyang's foreign ministry said in a statement Thursday.

Seoul, Tokyo and Washington have ramped up joint military drills in recent weeks, including large-scale naval maneuvers and anti-submarine exercises.

The US will redeploy the nuclear-powered USS Ronald Reagan to waters east of South Korea for a second visit in less than a month, Seoul said Wednesday.

North Korea's foreign ministry said in a statement carried by the official KCNA that this posed "a serious threat to the stability of the situation on the Korean peninsula."

Early on Thursday, South Korea's military said it had detected two short-range ballistic missiles launched from the Samsok area in Pyongyang towards the East Sea, also known as the Sea of Japan.

The first missile traveled 350 kilometers at a maximum altitude of around 80 kilometers, according to their analysis, with the second flying 800 kilometers at an altitude of 60 kilometers.

It appears to be the first time North Korea has fired missiles from Samsok, an official from Seoul's Joint Chiefs of Staff told reporters.

He added that they look like a "different type of short-range ballistic missiles" from previous launches.

Tokyo also confirmed the launches, with defense minister Yasukazu Hamada telling reporters that it was important not to "overlook the significant improvement of (North Korea's) missile technology."