The United States has designated a notorious drug-trafficking organisation in Colombia as a terrorist group.

The US Treasury Department added the group, known as Clan del Golfo or Gulf Clan, to its list of Foreign Terrorist Organisation (FTOs).

The designation came just hours after US President Donald Trump signed an executive order classifying the drug fentanyl as a 'weapon of mass destruction'.

The two moves are seen as a further ramping-up of the Trump administration's war on drugs, which has also included over 20 lethal strikes on boats suspected of transporting drugs in the Caribbean and the Pacific.

More than 90 people were killed in these strikes, raising legal and ethical concerns among experts.

Clan del Golfo is one of Colombia's largest cocaine-trafficking organisations and is also involved in smuggling migrants through the Darién Gap, a dangerous jungle area connecting Colombia and Panama.

In the subsequent announcement, US Secretary of State Marco Rubio indicated that the group is responsible for various terrorist attacks against public officials and civilians in Colombia, further justifying its FTO designation.

This designation complicates the recent peace negotiation efforts initiated by Colombia's President Gustavo Petro, who had reached an agreement with the Clan del Golfo just weeks before. As a result, relations between the Colombian administration and the Trump administration remain tense, with both sides publicly criticizing each other's actions.