SEOUL-- The United States has confirmed in an official letter that there is no gap between Washington and Seoul on how to denuclearize North Korea, Seoul's presidential office Cheong Wa Dae said Monday, partly dismissing concerns of what many view as an imminent U.S. attack on the communist North.

"We received a reply from the U.S. National Security Council last night, and it noted there was no difference of view between South Korea and the United States," a ranking Cheong Wa Dae official told reporters, while speaking on condition of anonymity.

The letter came hours after U.S. President Donald Trump said in a tweet that South Korea was "finding, as I have told them, that their talk of appeasement with North Korea will not work," apparently suggesting what many believed is a rift between the two allies.

Seoul asked the U.S. to verify what Trump's message suggested.

In a telephone conversation with his South Korean counterpart, White House security adviser H.R. McMaster said the U.S. will closely and transparently discuss all future measures with its South Korean ally, Cheong Wa Dae said.

"The U.S. side reaffirmed its firm commitment to the defense of South Korea, and the two sides agreed to take any future steps under close and transparent consultations between the two countries while working to come up with strong punitive measures against North Korea's nuclear test provocation based on their airtight cooperation together with the international community," it said in a press release.

The telephone conversation between McMaster and Chung Eui-yong, the head of the presidential National Security Office, marked the third of its kind since the communist North staged its latest nuclear test on Sunday.

South Korean President Moon Jae-in earlier insisted the allies were in complete agreement through their frequent and candid discussions on ways to rid the North of its nuclear ambitions.

In their last telephone conversation, held after North Korea fired a believed intermediate range ballistic missile over Japan last week, Moon and Trump agreed to put maximum pressure and sanctions on the North to bring the reclusive state back to the dialogue table, stressing the only and final objective of sanctions against the impoverished North was to resolve the nuclear issue peacefully.

Pyongyang conducted its sixth nuclear test Sunday.

When asked by reporters if he planned to attack the North, the U.S. president said, "We'll see."

Moon has declared there will be no war on the Korean Peninsula ever again, also insisting the U.S. will not take any action that might start an armed conflict on the peninsula without Seoul's consent and claiming that he and his U.S. counterpart have come to such an understanding.

Source: Yonhap News Agency