WASHINGTON (AP) — U.S. Secretary of State Marco Rubio on Thursday accused China of “bullying” by detaining or holding up dozens of Panama-flagged ships — though for a short period of time — after the Central American country seized control of two critical ports on the Panama Canal earlier this year from a subsidiary of a Hong Kong-based company.

China denies the allegations. Panama has been caught in a broader rivalry between the United States and China after U.S. President Donald Trump accused Beijing last year of running the Panama Canal. The Trump administration sees the critical maritime trade route as strategically important, both commercially and militarily, and Trump has talked about retaking the Panama Canal since his campaign.

“China’s decision to detain or otherwise impede Panama-flagged vessels engaged in lawful trade destabilizes supply chains, raises costs, and erodes confidence in the global trading system,” Rubio said on social media. “The United States stands with Panama against any retaliatory actions against its sovereignty and will always support our partners in the face of bullying.”

Of the 124 ships detained in Chinese ports for inspection in March, 92 — or nearly 75% — were Panama-flagged, according to public data from Tokyo MOU, a regional port state control organization comprising 22 member authorities in the Asia-Pacific region. The Panama-flagged ships were typically detained for a few days — as short as one day or as long as 10 days — before being released.

That is up drastically from the previous two months, when 19 out of 45 ships — or more than 40% — held in February were Panama-flagged, and 23 out of 71 — or over 30% — in January hung the Panama flag.

America’s “repeated wrongful allegations only reveal its attempt to take control of the canal,” said Liu Pengyu, spokesperson for the Chinese embassy in Washington. In a statement, he did not address the uptick in the number of Panama-flagged ships held up in Chinese ports.

It comes amid the backdrop of Panama’s supreme court ruling in January that the concession held by a subsidiary of Hong Kong’s CK Hutchison Holdings over the Balboa and Cristóbal terminals was unconstitutional.

The U.S. has pressured Panama and other Latin American countries to curb China’s sway in the Western Hemisphere, where Trump has said he would increasingly focus. The Trump administration has gotten involved in Latin American affairs more aggressively than the U.S. government has in decades, most dramatically by capturing Venezuela’s leader Nicolás Maduro in a military raid in January.

The Federal Maritime Commission in Washington has been tracking Panama-flagged vessels that are being detained or held up in Chinese ports.

“Secretary Rubio’s statement highlights the disruptive effects of the government of China’s actions against Panama-flagged vessels,” said Laura DiBella, chair of the commission. She said the commission “is not aware of any other country in recent history conducting vessel safety inspections and detentions in a punitive manner.”

Panama’s government has said APM Terminals, a subsidiary of the Danish group A.P. Moller-Maersk, would temporarily assume the administration of the terminals while a new contract is awarded. DiBella said that the Chinese Ministry of Transport had summoned Maersk to Beijing for high‑level discussions.

Panama’s government has sought to minimize the wider geopolitical tensions surrounding the ships. Officials did not respond to requests for comment about Rubio’s comments, but previously denied that the detentions had to do with disputes between China and Panama over the canal.

In March, Panama’s foreign minister, Javier Martínez, recognized that there had been an increase in detentions but said he believed they were “part of routine maritime industry practices, because detentions also occur in other ports and to other flags.”

“We want to maintain a respectful relationship with China,” he added.

After the ruling from the Panama supreme court in January, Chinese Foreign Ministry spokesperson Guo Jiakun said China would “take all measures necessary to firmly protect the legitimate and lawful rights and interests of Chinese companies.”

José Digeronimo, former president of the Panama Maritime Chamber, said actions with the ships could have a “huge impact” on Panama, which is a world leader in ship registries. The registries generate around $100 million for the government every year.

Digeronimo compared such registries to shipowners choosing passports, with owners registering their boats in places that “allow you to travel to the greatest number of countries without restrictions.” Harassment by Chinese authorities could put that in jeopardy, he said.

“If the world’s main exporter starts imposing restrictions for using the Panamanian flag, the last thing you’ll want is to have the Panamanian one,” Digeronimo said.

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Solís reported from Panama City. Associated Press writer Megan Janetsky in Mexico City contributed to this report.

Didi Tang And Alma Solís, The Associated Press