The Panamanian government has complained to the United Nations over US President Donald Trump’s “worrying” threats to seize the Panama Canal after more than two decades of the Central American country’s control over the interoceanic waterway.

The move was prompted after Trump claimed in his inaugural address that China was effectively “operating” the Panama Canal through its growing presence around the waterway, which the United States handed over to Panama at the end of 1999 under a treaty signed in 1977 by former president Jimmy Carter.

The US president, not ruling out using military force to reclaim the canal, said, “We didn’t give it to China, we gave it to Panama and we’re taking it back.”

In a letter to UN Secretary General Antonio Guterres on Tuesday, the government in Panama City pointed to an article of the UN Charter precluding any member from “the threat or use of force” against the territorial integrity or political independence of another.

The letter urged Guterres to refer the matter to the UN Security Council, without asking for a meeting to be convened.

Panama’s President Jose Raul Mulino had denied earlier that any other nation was interfering in the canal, which he said was operated on a principle of neutrality.

“The canal is and will remain Panama’s,” Mulino said in response to Trump’s threats.

The canal’s administrator, Ricaurte Vásquez, too, said this month that China is not in control of the canal and that all nations are treated equally under a neutrality treaty.

Vásquez said Chinese companies operating in the ports on either end of the canal were part of a Hong Kong consortium that won a bidding process in 1997. He added that US and Taiwanese companies operate other ports along the canal as well.

Since 2000, the waterway has contributed more than $30 billion to Panama’s state coffers, including nearly $2.5 billion in the last fiscal year.

The new US Republican president has been raising pressure for weeks over the canal, through which 40 percent of US container traffic travels.

The US military invaded Panama on December 20, 1989 to remove the country’s dictator Manuel Noriega.

Some 27,000 troops were tasked by then-president George H.W. Bush with capturing Noriega, protecting the lives of Americans living in Panama and restoring what they claimed as democracy to the country with the aim of seizing control of the Panama Canal a decade later.

Last month, Panamanians celebrated the 25th anniversary of the handover and days later they commemorated the deaths of 21 of their compatriots who died at the hands of the US military decades earlier.