The president of the United States said he was not ruling out decertifying Colombia as a drug-war partner due to the recent sharp rise in coca production in the Andean nation.

Donald Trump, in a memorandum to US Secretary of State Rex Tillerson, identified 22 countries - most of them in the Latin American and Caribbean region - as "Major Illicit Drug Producing and Major Drug-Transit Countries."

That list of countries, which does not necessarily reflect the counter-narcotics efforts of their governments or their level of cooperation with the US on illegal drug control, comprises Afghanistan, the Bahamas, Belize, Bolivia, Burma, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, India, Jamaica, Laos, Mexico, Nicaragua, Pakistan, Panama, Peru and Venezuela.

Bolivia and Venezuela were designated as countries that had "failed demonstrably" during the previous 12 months to adhere to their obligations under international counter-narcotics agreements.

But the novelty of this year's memorandum was the decision to threaten Colombia, Washington's closest ally both in the Latin American region and in the fight against drug trafficking, with decertification.

The US "seriously considered designating Colombia as a country that has failed demonstrably to adhere to its obligations under international counter-narcotics agreements," the presidential memorandum stated, citing the "extraordinary growth of coca cultivation and cocaine production over the past 3 years, including record cultivation during the last 12 months."

The White House's Office of National Drug Control Policy estimated in March that Colombian cocaine cultivation rose from 159,000 hectares (613 sq. miles) in 2015 to 188,000 hectares in 2016, adding that that latter figure was a record high.

"Ultimately, Colombia is not designated because the Colombian National Police and armed forces are close law enforcement and security partners of the United States in the Western Hemisphere," Wednesday's memo said, adding that Bogota had restarted some coca-eradication efforts that had been significantly cut back beginning in 2013, coinciding with the start of peace talks with leftist guerrillas.

Decertification, however, remains an option, the memo said.

But Colombia on Thursday defended its anti-narcotics efforts and said the US rebuke was unwarranted.

"Colombia is without a doubt the country that has most combated (illegal) drugs and that has had the most success on that front. No one needs to threaten us to confront this challenge," President Juan Manuel Santos' administration said in a statement, adding that the Andean nation had shown its commitment to tackling the drug problem over a period of more than 30 years and paid a very high cost in human lives.

"Colombia once again reiterates that commitment and underscores its willingness to continue cooperating with the consumer countries to defeat this scourge," it added.