Russian President Vladimir Putin said on Thursday that Moscow had no choice but to build up its military in response to US anti-missile defense in Alaska and South Korea, according to Reuters and Tass News Agency.

Putin said at an economic forum in St Petersburg that Russia could not stand “idly by” while others increased their military capabilities in the Far East, noting that Moscow was particularly alarmed by the deployment of the US THAAD anti-missile system in South Korea.

"This destroys the strategic balance in the world," Putin said.

"What is happening is a very serious and alarming process. In Alaska, and now in South Korea, elements of the anti-missile defense system are emerging. Should we just stand idly by and watch this? Of course not. We are thinking about how to respond to these challenges. This is a challenge for us."

He further argued that even if the DPRK terminates its tests and missile program, the deployment of THAAD will continue under a different pretext or without any pretexts at all.

Yonhap reported on Thursday that the new administration in Seoul intends to seek a thorough environmental study on the US THAAD system before deploying four additional launchers, and the full deployment of the anti-missile system could take more time if the study is to be completed.