North Korea fired off its second missile test in a week on Sunday, sending a medium-range ballistic missile into the waters off its east coast, according to statements from the U.S., South Korean and Japanese governments.

South Korea, which called the launch “reckless and irresponsible,” said the missile flew about 500 kilometers (300 miles) from an area near Pukchang, in western North Korea.

Japanese Defense Minister Tomomi Inada said the missile hit the water about 350 kilometers (217 miles) from the east coast of North Korea.

She said the missile did not go higher than 1,000 kilometers (620 miles), according to preliminary data.

Altitude was key to the test a week earlier, which analysts called North Korea’s most successful ever in its quest to develop ballistic missiles that can carry nuclear warheads.

The May 14 test reached an altitude of more than 2,100 kilometers (1,300 miles), according to North Korea.

Analysts said that test showed gave North Korea critical information on developing a re-entry vehicle for nuclear warheads and showed Pyongyang had a missile capable of striking the U.S. territory of Guam.

A White House official said the projectile in the latest test was a medium-range ballistic missile, a system that North Korea tested in February.

Analysts say North Korea’s tests may be providing information that will bring it closer to its goal of developing an intercontinental ballistic missile that could possibly threaten the U.S. mainland.

After the May 14 test, Melissa Hanham, senior research associate at the James Martin Center for Nonproliferation Studies in California, said it could be a stepping stone to a longer-range weapon.

Read more: CNN