North Korea fired two ballistic missiles into the Sea of Japan early Sunday morning, Japanese and South Korean authorities said, conducting its seventh launch in two weeks as the isolated, nuclear-armed country maintained a rapid clip of weapons tests not seen in years.

Japanese State Minister for Defense Toshiro Ino said that the missiles were believed to have landed in waters outside Japan’s exclusive economic zone, which extends 200 nautical miles (370 kilometers) from its coast. He said both missiles had flown about 350 km, hitting a maximum altitude of around 100 km, with the first fired at around 1:47 a.m. and the second about six minutes later.

Ino slammed the “unprecedented frequency and new manner of launches,” adding that the Defense Ministry was continuing to analyze the missiles, including the possibility that both could have been submarine-launched weapons.