By Katharine Jackson and Michael Martina

WASHINGTON, April 2 (Reuters) – U.S. Secretary of State Marco Rubio expressed serious concerns on Thursday about China's recent detentions of Panama-flagged ships following a ruling from a Panamanian court. He suggested that these actions could threaten the rule of law in Panama.

Last week, the U.S. Federal Maritime Commission announced it was closely observing a spike in detentions of Panama-registered vessels in China, which seems to be linked to the court's decision against the Hong Kong-based port operator, CK Hutchison.

Rubio stated, “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.”

In late January, Panama's Supreme Court overturned the legal setup that allowed CK Hutchison's Panama Ports Company to manage the Balboa and Cristobal terminals on both sides of the Panama Canal.

This cancellation came after increasing pressure from the U.S. to reduce Chinese influence around the strategically important canal, which carries about 5% of global maritime trade.

The Chinese embassy in Washington did not respond immediately to Rubio's statement. Beijing has previously stated its strong opposition to the court’s ruling against Hutchison's port concessions, labeling it an "act of bad faith."

CK Hutchison, which has operated the ports for almost 30 years, disagrees with the court ruling, accused Panamanian officials of unlawfully seizing assets, and has initiated an international arbitration case against Panama, seeking over $2 billion in damages.

Rubio emphasized, “This sovereign ruling upheld transparency, the rule of law, and held private operators accountable to the public interest.”

He added that the U.S. “stands firmly” with Panama and looks forward to enhancing economic and security cooperation.

The FMC noted that China's detentions of Panama-registered vessels have exceeded historical averages, with Lloyd's List Intelligence reporting nearly 70 detentions since March 8.