PANAMA CITY — Panama on Tuesday marked the 25th anniversary of the United States' 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 moment of silence was held in memory of Carter, whose endorsement of the treaty set up transfer of the canal to Panama on Dec 31, 1999.

Former Panamanian president Mireya Moscoso, who oversaw the symbolic turn-of-the-century handover, told Agence France-Presse 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".

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

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

"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.

Francisco Cedeno, a 51-year-old graphic designer, described Trump's threats as "completely nonsensical".

"He should first try to resolve his country's many problems and forget about the canal," Cedeno said.

An estimated 5 percent of global maritime traffic passes through the Panama Canal, which was inaugurated in 1914 and allows ships to avoid the long, hazardous route around the southern tip of South America.

The canal generates 6 percent of Panama's national economic output and 20 percent of its fiscal revenues.

Since 2000 it has pumped around $28 billion into the state coffers.

Agencies via Xinhua