SEOUL (THE KOREA HERALD/ASIA NEWS NETWORK) - The first US-Japan summit of the Joe Biden administration, as expected, dealt with the need for a united front against China as its top priority.

The leaders of both countries focused on putting pressure on China in many areas, including technology.

They also reaffirmed their commitment to the complete denuclearisation of North Korea.

The two leaders agreed on the importance of trilateral cooperation among the US, South Korea and Japan in security and prosperity.

Japan got closer to the US despite the growing threat from China.

These developments sound a warning to South Korea ahead of its summit with the US late next month, given its different viewpoints on North Korea and China.

In the South Korea-US foreign and defence ministerial meeting in March, for example, the Moon Jae-in government revealed a different view on the expression "the denuclearisation of North Korea."

At a news conference after the meeting, South Korean Foreign Minister Chung Eui-yong said it was "more correct" to speak of the denuclearisation of the Korean Peninsula.

The Biden administration emphasises the "denuclearisation of North Korea" while the Moon government sticks to the "denuclearisation of the Korean Peninsula," effectively the same expression used by Pyongyang.

Citing this expression, the North demands that the South give up developing nuclear weapons and that the US cease to provide a nuclear umbrella for the South.

But the North broke its promise to denuclearise the Korean Peninsula and itself has developed nuclear weapons. It is questionable if the South is playing into the hands of North Korea.

US Secretary of State Antony Blinken mentioned pressure options as well as diplomacy. Mr Biden once said he could meet with North Korea's leader, Kim Jong-un, if the latter were to take steps toward denuclearisation.

The new US stance differs from the Moon administration's "peace process for the Korean Peninsula," an overarching policy concept of inducing the denuclearisation of North Korea by offering incentives first, such as by easing sanctions and making exceptions as needed.

Though Washington took a different tack on Pyongyang, Seoul is trying to revive dialogue between the US and North Korea as an extension of their 2018 summit in Singapore.

The North has declared itself a nuclear state. And yet the Moon government seems to believe the North Korean leader still has the will to denuclearise through dialogue with Washington. Dialogue is important, but whether it is the only solution needs to be reviewed.

North Korea's human rights record is especially burdensome for the Moon government in light of the differences with the US administration.

South Korea has not co-sponsored a United Nations resolution condemning North Korea's human rights violations for three consecutive years.

A US bipartisan commission recently hosted a human rights hearing on South Korea's decision to criminalise anti-North Korea leafleting.

Its different views on China are worrisome, too.

The leaders of the US and Japan dealt with "peace and stability across the Taiwan Strait," a sensitive issue for China, in their joint statement.

But Foreign Minister Chung went to Xiamen, a Chinese city close to Taiwan, for a meeting with Chinese Foreign Minister Wang Yi.

It was Mr Chung's first overseas trip since he took office. They discussed a possible visit to South Korea by Chinese President Xi Jinping. The Moon administration had invited Mr Xi in the past, but Mr Xi has not visited South Korea yet.

Mr Moon congratulated Mr Xi on the 100th anniversary of the foundation of the Chinese Communist Party. He praised China.

It is not difficult to guess how states in the free world now scrimmaging against China must see the Moon administration.

The US-Japan summit reaffirmed that the top priority of US diplomacy was the containment of China. The US is very likely to demand that its ally South Korea join a grand alliance to keep China in check.

The US-Japan summit effectively forewarned that it will become difficult to keep appeasing North Korea and walking a diplomatic tightrope between the US and China.

Mr Moon's first summit with Mr Biden should be an occasion to tighten the US alliance, which had slackened over the past four years, and narrow differences on North Korea and China.

If South Korea cannot speak in chorus with its ally, it will not only lose confidence from the US, but will also likely be treated poorly by Beijing in the long run.

Alliance-centric diplomacy is urgent to secure some latitude between the two superpowers.

• The Korea Herald is a member of The Straits Times media partner Asia News Network, an alliance of 23 news media organisations.