China on Monday raised pressure on South Korea to oppose the US' possible deployment of an advanced missile defence asset to Korea and be a founding member of the Asian Infrastructure Investment Bank, putting Seoul in a tricky diplomatic position.
Visiting Chinese Assistant Foreign Minister Liu Jianchao urged Seoul to respect Beijing's "attention to and concerns" over Washington's possible dispatch of the Terminal High-Altitude Area Defence system here, which Beijing argues could threaten its security.
"Beijing would be grateful (to Seoul) should it think of China's attention and concerns importantly," Liu told reporters in Seoul after holding consultations with Seoul's Deputy Foreign Minister Lee Kyung-soo over a series of bilateral and regional issues.
"We hope that the US and South Korea will make an appropriate decision over the potential deployment of THAAD," he added, noting the two sides held "very candid and free" talks over the issue.
As for Seoul's participation in the creation of the AIIB, Liu renewed Beijing's calls on Seoul to join the China-led initiative as a founding member.
Seoul has been cautious about its participation amid strong opposition from Washington which suspects the AIIB is a Chinese attempt to revise the regional financial order that has been led by the US and Japan.
But Seoul has to make its decision by the end of the month should it want to join the negotiations for the bank's Articles of Agreement.
Liu came to Seoul in return for Lee's visit to Beijing last December. The day after Liu arrived here, US Assistant Secretary of State for East Asian and Pacific Affairs Daniel Russel also visited Seoul to discuss pending issues with Korean officials.
The visits by the senior officials from Beijing and Washington fueled already tense public debate over the issues surrounding the THAAD and AIIB.
As for the THAAD issue, Seoul has maintained "strategic ambiguity."
It has said THAAD, a core asset of the US global multilayered missile shield programme, could be helpful for the defence of the South.
But it has made it clear that there has been "no request" from the US, "no consultations" with the ally and "no decision" reached.
Chinese officials including Chang Wanquan have repeatedly expressed their opposition to THAAD, apparently suspecting that the US may consider using the system not only against North Korea, but also against other potential adversaries such as China and Russia.
The Korean public has been divided over the THAAD issue: Some argue that strictly from the standpoint of security interests, Seoul should allow the US Forces Korea to install an additional missile defence system here.
But others argue it is inappropriate to make a decision to undermine China's security interests, while seeking greater economic relations through trade and exchanges with China.
The AIIB issue has become more complicated after Britain decided to join the AIIB last week, a decision that frustrated the US, Britain's core ally. Australia and France are also reportedly considering their participation.
During an interview with a local daily, Seoul's Foreign Minister Yun Byung-se said that Seoul would make a "balanced judgement" in consideration of its interests, and that it would not bow to any outside pressure.
Experts say that Seoul should try to persuade Washington and Beijing of its hopes to prevent the issues from harming bilateral ties, and take careful diplomatic steps based on its prudent calibration of national interests.
"It is a matter of how we can persuade China and the US to understand our position. Rather than dithering over the issues or making blunt decisions that would provoke any of them, we should explore ways to persuade them in a low-profile and tenacious manner, and very cogently," said Suh Jin-young, professor emeritus at Korea University.
"We should strive to gain their understanding by continuing to persuade them of our position. This calls for Seoul's cautious, prudent and sophisticated diplomacy."