TOKYO – North Korea launched a ballistic missile Tuesday morning that flew over the northern Japanese island of Hokkaido, public broadcaster NHK reported. The government issued an alert for residents in some prefectures to take cover.

Although North Korea has sent a missile over Japan once before – in 1998 – this launch comes at a time of heightened tensions. Pyongyang has been threatening to fire a missile over Japan and into the waters around the American territory of Guam.

“We’ll make the utmost effort to protect the public,” a visibly agitated Japanese prime minister, Shinzo Abe, told reporters at his office early Tuesday morning. NHK showed Patriot missiles lined up in Japan, a staunch U.S. ally, ready to shoot down any incoming missiles.

The Japanese government convened an emergency national security council meeting for 8 a.m. to discuss the threat.

The missile was launched at 5:58 a.m. Japanese time from a site at Sunan, north of Pyongyang. Sunan is the location of the country’s main international airport.

There was initial confusion over how many missiles were fired. Japan reported that three missiles had been launched, but later clarified to say that it thought one missile had been launched but that it had broken into three parts during flight.

The missile flew over Hokkaido at 6:06 a.m. It traveled 733 miles to land in the Pacific Ocean east of Hokkaido’s Cape Erimo, NHK reported.

South Korea’s joint chiefs of staff also confirmed that the missile had passed over Japan.

Tuesday’s launches, on the heels of three short-range missiles fired Saturday, come amid ongoing joint exercises between the United States and South Korean militaries, exercises that North Korea always strongly protests because it considers them preparation for an invasion.

The launches mark a dangerous new escalation from Kim Jong Un’s regime.

Kim – who has ordered the launch of 18 missiles this year alone, compared to the 16 missiles his father, Kim Jong Il, fired during 17 years in power -has defied international calls to stop his provocations.

Missile launches and nuclear tests are banned by the United Nations Security Council so the North Korean action consistutes a violation that will elicit more angry condemnation.

But Kim has pressed ahead unrelentingly, making strides with his missile program.

Last month, North Korea launched two intercontinental ballistic missiles theoretically capable of reaching the mainland United States.

Kim’s regime had been threatening to fire a missile to pass over Japan and land near Guam, the American territory in the Pacific Ocean that is home to two huge U.S. military bases, by the middle of this month. However, Kim later said that after reviewing the plans, he would “watch the Yankees a little longer” before making a decision whether to launch.

North Korea listed prefectures including Hiroshima, Ehime and Kochi as on the flight path. But Tuesday’s missile went in the other direction, north over Hokkaido and away from Guam.

After the Guam threat, President Donald Trump has warned North Korea that “things will happen to them like they never thought possible” should the isolated country attack the United States or its allies.