North Korea launched two ballistic missiles early Sunday, according to authorities in neighboring countries, the eighth such launch by Pyongyang in recent days, adding to broad concern in Washington and its allies in Tokyo and Seoul.

Officials in South Korea’s capital have claimed that the North’s missile launches may indicate that it is closer than ever to restarting nuclear testing for the first time since 2017, with preparations at its test site being seen for months.

Both of Sunday’s missiles reached an altitude of 100 km (60 miles) and covered 350 km (218 miles), Japan’s state minister of defence, Toshiro Ino, told reporters.

The first was fired at about 1:47 a.m. (1647 GMT) and the second some six minutes later.

They fell outside Japan’s exclusive economic zone, and authorities were looking into what type they were, including the possibility that they were submarine-launched ballistic missiles, he added.

The U.S. military said it was consulting closely with allies and partners following the launches, which it said highlighted the “destabilizing impact” of the North Korean nuclear arms and ballistic missile programs.

Still, the United States assessed that the latest launches did not pose a threat to U.S. personnel or American allies.

“The U.S. commitments to the defence of the Republic of Korea and Japan remain ironclad,” the Hawaii-based U.S. Indo-Pacific Command said in a statement.

The latest missile launches from the Muncheon area on North Korea’s east coast are a “serious provocation” that harms peace, South Korean authorities said.

On Tuesday, North Korea test-fired a ballistic missile farther than ever before, sending it soaring over Japan for the first time in five years and prompting a warning to residents there to take cover.

Ino said Tokyo would not tolerate the repeated actions by North Korea. The incident was the seventh such launch since Sept. 25.

Japan’s foreign ministry said the nuclear envoys of the United States, South Korea and Japan held a telephone call and shared the view that the North’s ballistic missile launches threatened the peace and security of the region and the international community, besides posing a civil aviation risk.

North Korea, which has pursued missile and nuclear tests in defiance of U.N. sanctions, said on Saturday its missile tests were for self-defence against direct U.S. military threats and had not harmed the safety of neighbours.

“Our missile tests are a normal, planned self-defence measure to protect our country’s security and regional peace from direct U.S. military threats,” said state media KCNA, citing an aviation administration spokesperson.

South Korea and the United States held joint maritime exercises on Friday, a day after Seoul scrambled fighter jets in reaction to an apparent North Korean bombing drill.

The United States also announced new sanctions on Friday in response to North Korea’s latest missile launches.