The FBI will take part in the investigation into three people linked to the US Consulate being killed last weekend in this border city near El Paso, Texas, Mexican authorities said.

'In Ciudad Juarez are several FBI (Federal Bureau of Investigation) agents who came to collaborate in the investigation of the murder of the consular official, her husband and the husband of another (consulate) employee,' a source in the Chihuahua state Attorney General's Office said.

US consular official Lesley Ann Enriquez and husband Arthur H. Redelfs, a detention officer at the El Paso County Jail, were killed Saturday by gunmen who fired on their vehicle on a busy street in Juarez.

The couple's baby, riding in the backseat, was not harmed.

Mexican citizen Jorge Alberto Salcido, the husband of another consulate employee, died in a similar attack minutes later.

Enriquez and Redelfs were US citizens residing in El Paso. They drove to Juarez last Saturday for the birthday party of another consulate employee, an event also attended by Salcido and his wife.

A spokesperson for the US Consulate confirmed Monday that personnel from the FBI and other federal law-enforcement agencies were in Juarez 'to evaluate the situation and establish security strategies'.

Mexican authorities suspect Saturday's killings were the work of a gang known as Los Aztecas, described as the armed wing of the Juarez drug cartel.

Mexican head of state Felipe Calderon voiced indignation about the murders and stressed authorities's determination to track down the perpetrators, while US President Barack Obama said he was 'deeply saddened and outraged' over the killings.

Juarez, where 1,600 people were killed in 2008 in violence attributed to organised crime, is a major battlefield in a struggle for dominance among Mexico's drug cartels.