WASHINGTON (AP) — President Donald Trump and his South Korean counterpart spoke on the phone Monday morning for the first time since North Korea boasted of another nuclear test.

Trump and South Korean President Moon Jae-in agreed to remove the limit on the payload of South Korean missiles as part of the countries' response to the North's move on Sunday, South Korea's presidential office said in a statement. The North claimed it had detonated a hydrogen bomb underground.

Both leaders also agreed that the latest test was a grave provocation that was "unprecedented."

The phone call came as the U.N. Security Council was holding its second emergency meeting in a week on the subject. Defense Secretary Jim Mattis on Sunday said the U.S. will answer any threat from the North with a "massive military response."

Trump has grown increasingly frustrated with the response of other countries to North Korean provocations. Over the weekend, he threatened to halt all trade with countries doing business with the North, a veiled warning to China, and faulted South Korea for its "talk of appeasement."

Trump is also considering triggering a withdrawal from a free trade agreement with South Korea, a business lobbying group said Saturday, raising concerns about a move that could cause a fresh economic rift between allies at a moment of heightened tensions with a common foe.