Panamanian officials offer concessions on Rubio’s first overseas stop, but say they cannot negotiate on control of the waterway.

Secretary of State Marco Rubio is arguing that the presence of two Hong Kong companies and other Chinese firms violates a treaty Panama has with the U.S.

On his first trip overseas as the top US diplomat, Rubio took a guided tour of the canal accompanied by its Panamanian administrator as a South Korean-affiliated oil tanker and Marshall Islands-flagged cargo ship passed through the vital link between the Atlantic and Pacific oceans.