Paraguayan anti-drug prosecutor Marcelo Pecci was shot dead execution-style Tuesday while honeymooning on a Colombian Caribbean island by attackers who fled by sea, police and his widow said.

Paraguay's president denounced the crime as a "cowardly murder" and a fellow prosecutor said the modus operandi was reminiscent of "the mafia."

Pecci, 45, was felled by two shots while relaxing on a beach on the idyllic tourist island of Baru, according to his wife, Paraguayan journalist Claudia Aguilera.

The couple got married on April 30 in the nearby city of Cartagena.

"Two men attacked Marcelo. They came (by sea) in a small boat, or on a jet ski, the truth is I did not see well," Aguilera told the El Tiempo newspaper.

One of the assailants got out and "without a word he shot Marcelo twice, one (bullet) hit him in the face and another in the back," she described.

Aguilera, who is pregnant, said her husband of fewer than two weeks had not received any threats.

The Decameron Hotel, where the couple was staying, said in a statement that "assassins arrived on the beach... and attacked and murdered one of our guests."

The motive for the killing was not immediately known, but Paraguayan prosecutor Augusto Salas, a colleague of Pecci, said the attack appeared "typical of the (drug) mafia, so that is what I will think until the contrary is proven."

Colombian police chief Jorge Luis Vargas said five homicide investigators have been dispatched to Baru and will receive backing from Paraguayan and US experts.

"There is information being collected... that will help us identify those responsibly," Vargas said.

Late Tuesday, Colombian police released a photo of one of the presumed attackers, wearing black Bermuda shorts and a beige Panama hat.