Image copyright Reuters Image caption "El Chapo" stared calmly ahead in court during Thursday's testimony

Mexican drug kingpin Joaquín "El Chapo" Guzmán personally tortured and murdered his rivals, his former bodyguard has said at a trial in New York.

In the most gruesome testimony to date, Isaias Valdez Rios described seeing "El Chapo" brutally beat at least three men before shooting them.

Guzmán denies charges including trafficking and money laundering. If guilty, he could be jailed for life.

The ex-boss of the Sinaloa cartel was held in 2016 after escaping from jail.

He used a tunnel to leave the prison in Mexico but was arrested five months later and extradited to the US in 2017.

"El Chapo", aged 61 and facing 17 charges, stared impassively in court during Thursday's testimony by his ex-bodyguard, correspondents say.

The trial, which opened last November amid high security, is expected to last about four months.

Prosecutors say the Sinaloa cartel is the biggest supplier of drugs to the US.

WARNING: CONTENT BELOW MAY BE UPSETTING

What did the bodyguard say?

Mr Valdez Rios told the court he had personally witnessed "El Chapo" murder three members of rival drug cartels.

In one incident, he said two people originally from Sinaloa who had joined the rival Los Zetas cartel were deemed traitors and rounded up by Guzmán's hitmen.

For more than three hours the drug lord brutally beat them, the witness said.

"They were completely like rag dolls - their bones were totally broken. They could not move. And Joaquin was still hitting them with the branch and his weapon too," Mr Valdez Rios said.

The two men were later driven to an area where they could see a large bonfire.

There, the jury was told, "El Chapo" cursed each one before shooting them in the head with his rifle.

The leader of the Sinaloa cartel ordered that they be thrown in the bonfire, telling his men that he did not want any bones to remain, the former bodyguard said.

Image copyright AFP/Getty Images Image caption Joaquín "El Chapo" Guzmán was extradited to the US by the Mexican authorities in 2017

The third man murdered by "El Chapo" was a member of the Arellano Felix cartel.

"He had burns made with an iron on his back, his shirt was stuck to his skin. He had burns made with a car lighter all over his body. His feet were burned," the witness said.

The man was then locked in a wooden structure for days. It was only then that the man was brought blindfolded with his hands and legs tied to a graveyard.

"El Chapo" started to interrogate him, and while he was responding, shot him with his handgun.

The man was still gasping for air - but he was dumped in a hole and buried alive, Mr Valdez Rios said.

The witness also said that he had himself narrowly avoided being killed because at one point the drug lord suspected him of stealing his money.

Mr Valdez Rios, 39, has been held in a US jail since his arrest in 2014.

A former member of Mexico's special forces, he began working for "El Chapo" in the early 2000s.

He faces a long prison sentence on drug trafficking charges. By co-operating with prosecutors, he hopes to see his sentence reduced.