Colombia's president ramped up denunciations of Donald Trump's anti-drug air strikes and swatted aside US threats to freeze hundreds of millions of dollars in aid on Thursday.

Fueling a spat that threatens to shatter ties between the long-allied nations, Gustavo Petro said, "Mr Trump has slandered me and insulted Colombia."

Petro accused Trump of "carrying out extrajudicial executions" that "violate international law" by striking alleged drug-trafficking boats.

The US has destroyed nine vessels and killed at least 37 people in under two months, according to US government accounts.

"The deaths keep increasing like a taxi metre," said Petro.

At least one Colombian is among the dead, a fisherman who Petro now admits may have become involved in trafficking "intermittently" to escape poverty.

Colombia has publicly demanded that Washington halt the attacks, infuriating Trump, who has branded Petro a "thug" and drug trafficker.

As retribution, Trump has announced an end to hundreds of millions of dollars of US aid to Colombia and threatened tariffs on Colombian goods.

If enacted, the cuts would stifle decades of security cooperation to curb the flow of cocaine from the world's biggest producer, Colombia, to its biggest consumer, the United States.

Petro dismissed the impact of aid cuts, saying the cash goes to fund US non-governmental groups and to buy US arms.

"What happens if they take away the aid? In my opinion, nothing," he said.

The United States provided Colombia with almost US$750 million in aid in 2023, according to US figures.

There are growing fears among Colombia's allies that a withdrawal of US funds could harm years-long efforts to stop the country from sliding back into conflict.

Despite peace accords a decade ago, pockets of the country are still controlled by guerrillas, cartels, and other armed groups.

The United States and other donors provide military aid as well as funding for coca eradication and demobilisation projects. (AFP)