The U.S. State Department has expressed disappointment and concern over South Korea's decision to terminate its military information-sharing agreement with Japan.

Spokesperson Morgan Ortagus tweeted on Sunday that Washington is "deeply disappointed and concerned" over Seoul's decision to terminate the General Security of Military Information Agreement(GSOMIA).

Ortagus added the move will make defending South Korea "more complicated" and "increase risk to U.S. forces." This is the first time the U.S. has referenced American troops regarding the cancellation of the intel-sharing deal.

Last Thursday, Seoul announced it would pull out of GSOMIA amid an escalating diplomatic and trade row with Tokyo stemming from colonial-era disputes.

In a rare public rebuke against Seoul, U.S. Secretary of State Mike Pompeo expressed disappointment in the decision, adding Washington is urging its two allies to continue their engagement.