US General Pledges to Defend Japan From NKorean Attack

America's top military official reiterated Friday his country's pledge to defend Japan against a North Korean missile attack, as western Japan carried out a test of an emergency alert system.

"I think we made it clear to North Korea and anyone else in the region that an attack on one is an attack on both of us," Joseph Dunford, the chairman of the Joint Chiefs of Staff, said in Tokyo.

North Korea has threatened to test-fire missiles that would fly over Japan and land in waters off the U.S. territory of Guam. The U.S. is treaty-bound to defend Japan from outside attacks.

Dunford and his Japanese counterpart Katsutoshi Kawano agreed to work together to strengthen missile defense systems. The U.S. general is on the last stop of an Asia tour that took him to China and South Korea and has been dominated by talk of the North Korean threat.

Sirens wailed across nine prefectures in western Japan in the test of the emergency system. Twitter users in the region said the sirens didn't work in some areas.

The flight path of the North Korean missile test would cross that part of the country.