With North Korea’s unprecedented launch of eight short-range ballistic missiles (SRBMs) from several locations across the country earlier this week, Pyongyang has raised concerns in Tokyo that the nuclear-armed nation may add another dimension to its attempts to evade and overwhelm missile defenses.

Pyongyang fired off a barrage of missiles into the Sea of Japan in quick succession on Sunday from at least four sites, according to the South Korean military. At least one of the missiles was capable of flying in an irregular trajectory that could help avoid interception, according to the Japanese Defense Ministry.

More worryingly for Tokyo, Defense Minister Nobuo Kishi described the event — multiple launches from multiple locations over a period of about 35 minutes — as “unusual,” indicating that the government believes the latest moves represent a new and more serious threat to Japan than past missile tests.