South Korea is unable to pay an upfront sum in investment in the United States as US President Donald Trump has suggested under a deal to cut tariffs and is seeking an alternative solution, a presidential adviser in Seoul says.

Since a handshake deal by the allies' leaders in July to lower US tariffs to 15 per cent from 25 per cent, as Trump earlier imposed, South Korea has said the $US350 billion ($A535 billion) in investment would be in the form of loans and loan guarantees as well as equity.

Trump in remarks this week said South Korea would provide the investment "upfront," despite the government's contention that kind of outlay could plunge Asia's fourth largest economy into a financial crisis.

"The position we're talking about is not a negotiating tactic but rather it is objectivel

See Full Page