"China has now imposed a surge in detentions of Panama?flagged vessels in Chinese ports under the guise of port state control, far exceeding historical norms," the US Federal Maritime Commission said in a statement.

"These intensified inspections were carried out under informal directives and appear intended to punish Panama after the transfer of Hutchison's port assets," the statement added.

A Panamanian court declared in January that a contract that had allowed Panama Ports Company (PPC), a subsidiary of Hong Kong conglomerate CK Hutchison, to manage the Panama Canal ports of Balboa and Cristobal since 1997 was "unconstitutional."

The court ruling is the latest legal move to ripple through the waterway, which handles about 40 percent of US container traffic and five percent of world trade.

The Central American country has been swept up in broader tensions between Washington and Beijing, with US President Donald Trump claiming, without providing evidence, last year that China effectively runs the canal.

"Given that Panama?flagged ships carry a meaningful share of US containerized trade, these actions could result in significant commercial and strategic consequences to US shipping," the US body said.

According to the statement, the Commission has the authority to investigate "whether regulations or practices of foreign governments result in conditions unfavorable to shipping in the foreign trade of the United States."

Presidents Donald Trump and Xi Jinping are scheduled to meet on May 14 and 15 in Beijing for a summit largely focused on trade.

In February, PPC filed a lawsuit at the International Chamber of Commerce (ICC) in Paris seeking at least $2 billion in damages.