WASHINGTON, April 2 (Reuters) - Detentions of Panama-flagged vessels by China that followed a Panamanian court ‌ruling raise serious concerns, U.S. Secretary of ‌State Marco Rubio said on Thursday.

The U.S. Federal Maritime Commission (FMC) said ​last week it was closely monitoring a surge in detentions of Panama-flagged vessels in China that appears tied to a Panama court ruling against Hong ‌Kong-based CK Hutchison.

"China’s recent ⁠actions against Panama-flagged vessels raise serious concerns about the use of economic tools ⁠to undermine the rule of law in Panama, a sovereign nation and vital partner for global commerce," ​Rubio said ​in a statement.

Panama's Supreme ​Court in late January ‌invalidated the legal framework supporting the 1997 concession granting CK Hutchison's Panama Ports Company the right to operate the Balboa and Cristobal terminals on the Pacific and Atlantic sides of the Panama Canal.

The ‌cancellation followed mounting U.S. pressure ​to curb Chinese influence around ​the strategic canal, ​which handles about 5% of global maritime ‌trade.

"This sovereign ruling upheld transparency, ​the rule ​of law, and held private operators accountable to the public interest," Rubio said.

China has said ​it firmly opposes ‌the ruling against Hutchison's port concessions, calling ​it an "act of bad faith."

(Reporting by Katharine Jackson; ​Editing by Doina Chiacu)