South Korea said it would create a joint military unit with the United States, as a report suggested the contingent would target North Korea's weapons of mass destruction if a full-scale conflict broke out.
The mechanised unit led by a US major general would be set up in the first half of next year, the South's defence ministry said, as part of elaborate preparations for any future war between the two Koreas.
"It will be the first combined field combat unit to carry out wartime operations," a defence ministry spokesman said without elaborating on its mission.
He declined to confirm a Yonhap report that its remit would include eliminating weapons of mass destruction in the nuclear-armed North if war broke out.
The ministry said the contingent would have a joint office of US and South Korean staff in Uijeongbu, north of Seoul, where the US 2nd Infantry Division guards a strategically important area as a deterrent to an invasion by North Korea.
In the event of an all-out conflict, a mechanised South Korean brigade would join forces with the US division, which is armed with helicopters and other advanced weapons, it said.
"This would be a symbol of a strengthened military alliance between the allies," a military official said.
If fresh hostilities broke out, the US commander in South Korea would assume control of the South's 640,000 troops.
A transfer of command in a wartime setting was set for next year, which would allow South Korea control of its own troops, but Seoul wants a postponement, citing the increased threat from North Korea's nuclear and missile development.
In June, the North announced the successful test of new high-precision, tactical guided missiles, and later conducted a series of missile and rocket tests.
UN resolutions bar Pyongyang from conducting any launches using ballistic missile technology.