South Korea's deputy foreign minister met with his U.S. counterpart in Seoul on Tuesday to reaffirm their strong alliance and discuss North Korea's nuclear program, the foreign ministry said.
  

The meeting between South Korean Deputy Foreign Minister for Political Affairs Lee Kyung-soo and U.S. Assistant Secretary of State Daniel Russel came amid a mounting Washington-Beijing row over an advanced U.S. missile-defense system and a China-led Asian development bank.
  

Russel arrived in Seoul on Monday for a two-day visit, becoming the first U.S. ranking official to visit the country since U.S. Ambassador to South Korea Mark Lippert was injured by a knife-wielding attacker early this month.
  

Russel expressed the U.S. government's appreciation for cooperation and support from South Korea, which showed its seriousness in dealing with the injured U.S. envoy.
  

"The foundation of the alliance is rock-solid," Russel said at the start of the meeting, knocking on a wood table.
  

Upon arrival, Russel said that he will have talks over the "broad spectrum of alliance issues" with Seoul officials.
  

"We have a lot of work to do, a lot of very important work to do," Russel said Monday.
  

Russel's visit came as South Korea is struggling to walk a diplomatic tightrope between the United States, Seoul's key ally, and China, Seoul's largest trading partner, over the sensitive security issue.
  

His trip coincided with a trip by Chinese Assistant Minister of Foreign Affairs Liu Jianchao who, on Monday, expressed China's concerns about the possible deployment of an advance U.S. missile-defense system on South Korean soil.
  

The U.S. has expressed its hope to deploy a Terminal High-Altitude Area Defense battery in South Korea, where about 28,500 American troops are stationed.
  

Seoul and Washington have said there have been neither consultations nor a decision related to the THAAD deployment.
  

But China has explicitly voiced its opposition to Washington's possible deployment of a THAAD battery in South Korea, apparently out of concerns the move may be aimed at containing a rising China.
  

Liu also expressed hope Monday that South Korea will become a founding member of the China-proposed Asian Infrastructure Investment Bank.
  

Washington and Beijing have been sparring over the AIIB as the U.S. has raised concerns about the bank, citing its lack of transparency in decision-making processes.
  

China launched the AIIB late last year with 20 other nations as a counterbalance to the Asian Development Bank, led by the U.S. and Japan. The AIIB has not begun operations yet as details are still being worked out. Washington apparently has pressed its key ally Seoul to be cautious about joining the regional bank.
  

Seoul plans to decide whether to join the AIIB soon as China has said the deadline to become a founding member of the bank is the end of March. Britain announced its plan last week to join the bank, becoming the first Western country to do so. (Yonhap)