A senior U.S. official said on Thursday that defense cost-sharing negotiations between the U.S. and South Korea are not just about the cost but a matter of sharing the security burden. 

Assistant Secretary of State Clarke Cooper, who is in charge of the Political-Military Affairs Bureau at the State Department, made the remarks during a teleconference with reporters in Washington.

Regarding the stalled talks, Cooper said that it's been a continuous conversation. 

The assistant secretary said that while there was a pause, the U.S. is certainly re-approaching the issue, adding it is not just cost sharing, but the "burden sharing of the security of the Korean Peninsula."

He also stressed that Washington has shown "significant flexibility" in talks and that the two sides continue to work to find a "mutually acceptable agreement."