North Korean leader Kim Jong Un watched a ballistic missile launch test and ordered the country to improve nuclear attack capability by continuing to conduct more tests, the official KCNA news agency reported on Friday.

The report did not say when the test took place but it was likely referring to the launch of two short-range missiles by North Korea on Thursday that flew 500 km (300 miles) and splashed into the sea.

"Dear comrade Kim Jong Un said work ... must be strengthened to improve nuclear attack capability and issued combat tasks to continue nuclear explosion tests to assess the power of newly developed nuclear warheads and tests to improve nuclear attack capability," KCNA said.

Tension rose sharply on the Korean peninsula after the North conducted its fourth nuclear test in January and fired a long-range rocket last month leading to the U.N. Security Council to adopt a new sanctions resolution.

Conducting more nuclear tests would be in clear violation of U.N. sanctions which also ban ballistic missile tests, although Pyongyang has rejected them. North Korea has a large stockpile of short-range missiles and is developing long-range and intercontinental missiles.

The North Korean leader was quoted in state media on Wednesday as saying that his country had miniaturized nuclear warheads to mount on ballistic missiles. South Korea said it did not believe that North Korea had successfully miniaturized a nuclear warhead or deployed a functioning intercontinental ballistic missile.

Pyongyang has conducted four nuclear tests in the past decade and claimed to have successfully tested a hydrogen bomb in January but most experts expressed doubt saying the blast was too small to back up the assertion.

North Korea has issued nearly daily reports this week of Kim's instructions to fight South Korea and the United States as those two allies began large-scale military drills.

North Korea called the annual drills "nuclear war moves" and threatened to respond with an all-out offensive. Kim last week ordered his country to be ready to use nuclear weapons in the face of what he sees as growing threats from enemies.