The announcement followed a North Korean rocket launch that the US and its allies condemned as a covert ballistic missile test.
"It has been decided to formally start talks on the possibility of deploying the THAAD system to South Korea as part of steps to bolster the missile defence of the Korea-US alliance," said Yoo Jeh-Seung, the South's deputy defence minister for policy.
There has been speculation for years about the deployment of the Terminal High Altitude Area Defense (THAAD) system -- one of the most advanced in the world -- to the South, one of Washington's main Asian allies.
"The Korea-US alliance had no choice but to take such a defence action because North Korea staged a strategic provocation and is refusing to have a genuine dialogue on de-nuclearisation," Yoo said in a joint briefing with Lieutenant General Thomas Vandal, commander of the US Eighth Army based in the South.
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Vandal argued that it was "time to move forward" with the THAAD issue, claiming there was "growing support" in the South for its deployment.
But Yoo stressed the THAAD system -- if deployed -- would "operate only regarding North Korea".