Panama City, Panama - Panama on Tuesday marked the 25th anniversary of the US' handover of its interoceanic canal, a milestone overshadowed by President-elect Donald Trump's threat to demand control be returned to Washington.

The anniversary came two days after the death of former US president Jimmy Carter, who in 1977 signed the treaties that led to the vital waterway's eventual transfer decades later.

Panamanian President Jose Raul Mulino said at the anniversary ceremony, held at the Panama Canal Authority's headquarters, that "a sadness... fills us with the death of Jimmy Carter."

A minute of silence was held in memory of Carter, whose endorsement of the treaty set up the transfer of the canal – completed by the US in 1914 – to Panama on December 31, 1999.

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Former Panamanian president Mireya Moscoso, who oversaw the symbolic turn-of-the-century handover, said that "today we feel the same emotion" as on that occasion 25 years ago.

Neither Mulino nor the various other speakers at Tuesday's ceremony mentioned Trump and his recent threats in their speeches.

But the US President-elect has sparked anger among Panamanians by saying he will demand the canal "be returned to us" if Panama could not ensure its "secure, efficient, and reliable operation."

Trump has slammed what he called "ridiculous" fees for US ships passing through the canal and has alleged, without evidence, that Chinese soldiers were "lovingly, but illegally, operating" the channel.

Panama's political class and many of its citizens have roundly rejected Trump's repeated threats.

The 1977 treaties "put an end to an era of subjugation and began a period of independence and dignity," said another former president, Martin Torrijos.

"Any attempt to reverse or violate our sovereignty will be condemned and rejected by all Panamanians," he added.

Mulino has ruled out negotiations with Trump over control of the canal and denied that China had any influence over it.

"There are no Chinese soldiers in the canal, for the love of God," he said last week.