Incoming US president Donald Trump on Saturday slammed what he called unfair fees for US ships passing through the Panama Canal and threatened to demand control of the waterway be returned to US control.

He also pointed to China’s growing influence around the canal, a concern for American interests as U.S. businesses rely on the passage to move goods between the Atlantic and Pacific oceans.

"Our Navy and Commerce have been treated in a very unfair and injudicious way. The fees being charged by Panama are ridiculous," he said in a post on his Truth Social platform.

"This complete 'rip-off' of our Country will immediately stop."

The Panama Canal, completed by the United States in 1914, was handed over to Panama under a 1977 agreement signed by President Jimmy Carter. Panama took full control in 1999.

"It was solely for Panama to manage, not China, or anyone else," Trump said. "We would and will NEVER let it fall into the wrong hands!"

He added that if Panama could not ensure "the secure, efficient and reliable operation" of the canal, "then we will demand that the Panama Canal be returned to us, in full, and without question."

Authorities in Panama did not immediately respond to Trump’s post.

Although he does not officially take office until next month, Trump has been asserting his political influence in the final days of President Joe Biden’s administration.

The real estate mogul had boasted on the campaign trail that, as an entrepreneur, he was uniquely positioned to advocate for U.S. business interests.

An estimated 5% of global maritime traffic passes through the Panama Canal, which allows ships traveling between Asia and the U.S. East Coast to avoid the long, hazardous route around the southern tip of South America.

The main users of the passage are the United States, China, Japan, and South Korea.

The Panama Canal Authority reported in October that the waterway earned record revenues of nearly $5 billion in the last fiscal year.