Well I think they are using US supplied missiles
No US tech in it. Korean missiles, be it A2A, SAM, cruise, or ballistic missiles all originate from the Russian technology transferred in the 90s, when Russia was desperate for cash.
The issue is that this missile range control agreement was signed in the 1980s, then the military dictator agreed to it in exchange for the US recognition of the dictator government.
Now that the ROK wants to extend the ballistic missile range to 1,000 km to strike Beijing, the US opposes it because of protest from Tokyo because the same missile too could strike Tokyo if turned around, and the Japanese government is asking the US government to oppose the ROK ballistic missile force build-up program.
Anyhow, this 550 km thing appears to have been leaked by the ROK government in order to flame the public opinion(The Korean public outrage and million-man protest in 2008 forced the US to revise the US beef to 3 years or younger, when the initial agreement had no restriction), as they need the public support to extend it to 800 km, which will still enable the ROK military to strike Beijing with land-based ballistic missiles. Otherwise the ROK government would have to invest in sub-launched ballistic missiles.
Inaccurate.
