The U.S. defense chief has once again highlighted the need for its allies to spend more on defense.
At an event by the Atlantic Council think tank on Tuesday, Mark Esper said the partnership with its allies will be effective if allies actively contribute to military deterrence.
He added there can be no free riders to common security.
Esper noted the progress NATO allies have made in meeting their pledge to spend at least two percent of GDP on defense.
Washington has also been demanding a sharp increase in the amount Seoul pays during their defense cost-sharing negotiations.