U.S. Commerce Secretary Howard Lutnick said Thursday that South Korea should either accept a bilateral trade deal struck in July, or pay tariffs, amid a deadlock in negotiations between the two countries on details of the deal. 

Speaking to CNBC, Lutnick said South Korea did not sign the deal when President Lee Jae Myung visited Washington last month and the U.S. did not talk about trade because Lee did not sign the paper. 

He said he thinks South Korean saw how Japan signed the contract and that "there's no flexibility."

Lutnick then stressed that South Korea should either accept the deal or pay tariffs.

His remarks are seen as pressure from the U.S. for South Korea to accept the framework deal reached on July 30 as working-level negotiations on the specifics of the deal earlier this week failed to make a breakthrough.