The US Treasury Department was known to have asked South Korean banks last month to comply with sanctions against North Korea.

US Treasury officials had conference calls with them on Sept. 20 and 21, Financial Supervisory Service Gov. Yoon Suk-heun said during a parliamentary audit Friday.

The US officials reportedly asked the banks whether they had business plans involving North Korea, emphasized that US sanctions against the North are still valid, and expressed hopes that the banks would not violate them.

It is unprecedented for US Treasury officials to contact South Korean banks, not its financial authorities, to give them such a warning.

The telephone meetings were held shortly after the joint South and North Korean declaration was announced Sept. 19 in Pyongyang. The US effectively warned the banks not to do business that would effectively relieve sanctions against North Korea before tangible achievements are made in denuclearizing it.

US Secretary of State Mike Pompeo telephoned Foreign Minister Kang Kyung-wha on Sept. 17, a day before President Moon Jae-in left for Pyongyang for his summit with Kim, and reportedly complained about planned military agreements between South and North Korea, which were then signed as part of the Sept. 19 declaration.

The Moon administration says it had sufficient prior consultations with the US military authorities about the agreements, but it is questionable whether the consultations were really sufficient and close. Pompeo’s complaints leave us wondering if Seoul and Washington are cooperating smoothly.

US President Donald Trump said Wednesday that South Korea would not lift sanctions on Pyongyang without US “approval.”

It was an expression of the US’ position in response to Kang’s comment that suggested the possibility of South Korea lifting sanctions it imposed on North Korea on May 24, 2010, for torpedoing a South Korean naval ship about two months earlier.

Kang suggested during a parliamentary inspection of her ministry that Seoul was considering easing the sanctions to encourage its denuclearization.

Large parts of the May 24 sanctions overlap with the UN sanctions. Easing the sanctions could amount to violating the UN sanctions.

With controversies rising over Kang’s and Trump’s remarks, Cheong Wa Dae said equivocally Thursday that it takes Trump’s words in a sense that Seoul and Washington are closely consulting each other about every matter on North Korea.

But his blunt words sound like an expression of dissatisfaction and concern over the South’s attitude toward the denuclearization of the North.

Trump firmly believes sanctions brought North Korea out to dialogue. He also thinks of sanctions as the leverage needed to make the North carry out denuclearization steps to the end. But Kang’s comments point in the opposite direction.

Discord between Seoul and Washington under the Moon administration is nothing new.

It could be heard when South Korean companies were found to have smuggled North Korean coal, the South Korean government set up an inter-Korean liaison office in Gaeseong, North Korea, and it attempted to send a train to the North to test an inter-Korean railroad it seeks to reconnect.

In this situation, Trump’s remarks sound as an open warning against any unilateral South Korean move to seek sanctions relief under the pretext of encouraging denuclearization.

Moon succeeded in rekindling US-North Korea dialogue. Trump’s second meeting with Kim is expected to take place in the next couple of months.

The US demands the North first take meaningful actions to denuclearize, while the North demands the US first take corresponding measures.

It is a misguided view that sanctions relaxation will encourage denuclearization. The Moon administration deserves credit for thawing inter-Korean ties and shifting the situation from confrontation to dialogue, but there are limits and risks to pushing for better relations with the North by easing or circumventing sanctions.

North Korea recently issued a joint statement with China and Russia calling for sanctions relief and phased denuclearization.

Close cooperation with the US is needed more than ever.