A senior US official on Tuesday brushed off Beijing's objection to the possible deployment of a US missile defence system in South Korea, saying North Korea's missile programme poses a "significant threat."

The comments by US Assistant Secretary of State Daniel Russel, who is visiting Seoul, came after China's Assistant Minister of Foreign Affairs Liu Jianchao expressed concern on Monday over the idea of a US missile defence system on South Korean soil.

Liu's statement followed similar comments made by Chinese Defence Minister Chang Wanquan during his visit to Seoul last month. China sees the system as designed to curb its own military might.

"I find it curious that a third country would presume to make strong presentations about a security system that has not been put in place and that is still a matter of theory," Russel told journalists after meeting with South Korean Deputy Foreign Minister Lee Kyung-Soo.

US military authorities say they have conducted "informal studies" to find suitable sites for a possible future deployment of a Terminal High-Altitude Area Defense (THAAD) battery. But they have stressed that no decisions have been made to deploy such a system.

Russel said South Korea and the United States face a "signficant threat from North Korea's growing ballistic missile programme", which he said the North pursues in violation of international laws.

"Our military authorities have responsibility to consider systems that would protect Republic of Korea (South Korea) citizens, protect the United States from that threat".

"How they do it when they do it is something that the experts will have to determine but I think that it is for the Republic of Korea to decide what measures it will take in its own alliance defence", he added.

Walking a diplomatic tight rope between China and the United States, South Korea remains ambivalent on the sensitive security issue, saying there have been neither consultations with the United States nor a decision on the matter.

South Korea's Defence Ministry Spokesman Kim Min-Seok on Tuesday condemned China's attempt to "influence" South Korea's security policy.

"Neighbours can have their own positions on the (possible) deployment of the THAAD system here by the US Forces Korea. But they should not try to influence our security policy," the spokesman told a regular briefing.

He didn't mention China by name, but the message was clear.

"We will make a decision based upon our own judgement after putting security interests before anything else if the US government asks for consultation," Kim stressed.

South Korea hosts some 28,000 US troops.

Separately, Russel also made a fresh call for China to present evidence that the China-proposed Asia Infrastructure Investment Bank (AIIB) meets international standards for governance and transparency.

"We would like to see that done in ways that are consistent with the principles, the standards, good governance and the transparency that have become hallmarks of truly multilateral development banks," he said.

China's Lui had expressed hope Monday that South Korea join as a founding member of the AIIB -- which Washington fears could be a rival to the World Bank and extend Beijing's power.