North Korea conducted its sixth and most powerful nuclear test on Sunday, which it said was an advanced hydrogen bomb for a long-range missile.

This marks a dramatic escalation of the regime’s stand-off with the United States and its allies.

The announcement from Pyongyang came a few hours after international seismic agencies detected a manmade earthquake near the North’s test site, which Japanese and South Korean officials said was around 10 times more powerful than the tremor picked up after its last nuclear test a year ago.

There was no independent confirmation that the detonation, which drew swift international condemnation, was a hydrogen bomb rather than a less powerful atomic device. But Japan’s Chief Cabinet Secretary Yoshihide Suga said Tokyo could not rule out the possibility that it was a hydrogen bomb.

The test is a direct challenge to U.S. President Donald Trump, who hours earlier had talked by phone with Japanese Prime Minister Shinzo Abe about the “escalating” nuclear crisis in the region and has previously vowed to stop North Korea developing nuclear weapons that could threaten the United States.

North Korea, which carries out its nuclear and missile programs in defiance of United Nations Security Council resolutions and sanctions, said in an announcement on state television that a hydrogen bomb test ordered by leader Kim Jong Un was a “perfect success”.

The bomb was designed to be mounted on its newly developed intercontinental ballistic missile (ICBM), the North said.

The head of the U.N.’s nuclear watchdog, IAEA Director General Yukiya Amano said the nuclear test was “an extremely regrettable act” that was “in complete disregard of the repeated demands of the international community”.

French President Emmanuel Macron said the international community must react firmly to this “new provocation”, and South Korean President Moon Jae-in said Seoul would push for strong steps to further isolate the North, including new UN sanctions.

Japan also raised the prospect of further sanctions, saying curbs on North Korea’s oil trade would be on the table.

China, North Korea’s sole major ally, said it strongly condemned the nuclear test and urged Pyongyang to stop its “wrong” actions. The United States has repeatedly urged Beijing to do more to rein in its neighbor.