Harry Harris, commander of the US Pacific Command, has recently claimed that neither Seoul nor Washington has agreed to put a Terminal High Altitude Area Defense (THAAD) system in South Korea, adding that "the decision to discuss it is not necessarily a decision to do it, not yet." This is the second moderate remark from the US contrasting with the previous strong tones. Earlier last week, US Secretary of State John Kerry also made clear that the US is "not hungry or anxious to deploy THAAD," the installment of which is not necessary if North Korea denuclearizes.

The initial motivation for deploying THAAD on the Korean Peninsula stems from the US rebalancing to Asia-Pacific strategy, which aims at containing both China and Russia. But Washington needs a noble explanation to better implement and promote it. The growing nuclear and missile tests from Pyongyang have hence provided the White House a good excuse to do so.

However, after Chinese Foreign Minister Wang Yi met with Kerry in Washington last month, the two sides have come to an agreement on a draft resolution to impose tough sanctions against North Korea. Once the UN Security Council gives a green light to the draft, which will force the North to give up nuclear tests and go back to the negotiation table, Washington can no longer use Pyongyang as an excuse for deploying THAAD in South Korea.

The shift of the US attitude has put Seoul, which is hoping to increase its strategic advantages via THAAD, into a passive diplomatic situation.

South Korea's Dong-A Ilbo claimed that Washington's sudden turn of mood is putting Seoul in a tight spot and has awakened Seoul to the stark reality where China and the US are "capable of sidelining South Korea in addressing the issues on the Korean Peninsula."

Nevertheless, despite Seoul's worrying, the US change of stance is not that convincing to China. The issue of THAAD, a vital part of the US international strategy and a significant step to complete Washington's global missile defense system, has been discussed between the US and South Korea since the administration of former US president George W. Bush. The White House will not easily give it up. It is simply waiting and looking for the next opportunity.

If there will be any fierce resistance from Pyongyang, or increasing contradictions between Beijing and Washington over the South China Sea or the Diaoyu Islands due to the expansion of the US rebalancing to Asia-Pacific policy, the discussion over THAAD will be hyped up once again.

China is clearly aware of the impact of THAAD. Once deployed in South Korea, THAAD's radar range will extend well beyond the Korean Peninsula and effectively cover a large area of both China and Russia. By then, it would pose a serious security threat to not only North Korea, but also a wider region in Northeast Asia.

When China's national interests are under serious threat at its doorstep, Beijing will be bound to strike back, and THAAD will hence become the root of long-term trouble that haunts the entirety of Northeast Asia.

Washington is taking advantage of Seoul over this matter. The later should realize this, instead of constantly sounding China out over the issue of THAAD. It might wish that given its huge economic and trade volume with China, deploying the system would not severely jeopardize bilateral ties.

If it believes so and deems that China will only protest against it for a limited period, it would be wrong. In light of this, Beijing should clearly warn relevant stakeholders over the consequences of crossing its bottom line.

Both Washington and Seoul should learn to put themselves in China's shoes, and try to understand Beijing's concern over THAAD. If China deploys its own radar systems in Cuba or Canada, how will they respond?

The author is a professor on international politics at the College of Public Administration, Jilin University. opinion@globaltimes.com.cn