I doubt thatAs seen here, US did intervene in the selling of weapon and the possible tech that came with the weapon to Iran. This would also be the same case with Singapore selling weapons to China because most of Singapore's technology came from US.
US only intervene because they are against Iran's nuclear programme, the singaporans are selling them missle parts, this is highly sensitive material that contribute to Iran's development of nukes.
I believe China or Iran could easily get their hands on less sensative tech. Moreover, China is different from Iran, US has alreadly accept the fact we have nuclear weapons it is very unlikely to demand for missle parts. Maybe something else we need.