Officials of the FBI, DEA and three other agencies were sent to investigate the slayings of two Americans and a Mexican linked to the U.S. Consulate in Ciudad Juarez, Mexico over the weekend.

Lesley Enriquez, a U.S. consular official and her husband Arthur H. Redelfs -both Americans- were shot to death while they were driving home after a child's birthday party. Their baby daughter was traveling with them on the back seat but she was unharmed.

Separately, the husband of a Mexican employee at the U.S. consulate Jorge Alberto Salcido was also shot to death while he was driving with his two children. The children were wounded, according to officials.

All six of them have attended the same birthday party, according to the Department of State.

The tragedy of this weekend just underscores how severe and significant a danger this represents to Mexico, to the United States, to the hemisphere, State Department spokesman P.J. Crowley said in Washington.

The move comes as U.S. Secretary of sate Hillary Clinton and President Barack Obama pledged to work tirelessly with Mexican authorities to bring the killers of American citizens to justice.

Following the incident, Mexican President Felipe Calderon was scheduled to visit Ciudad Juarez today, his third visit to the violent city in less than two months.

The U.S. consulate closed Monday for a Mexican holiday and remained closed on Tuesday to review its security posture.

It is believed that the killings were carried out by a local gang known as Los Aztecas, which has ties with the Juarez drug cartel.

Drug-related attacks to U.S. diplomats are rare.  Although Mexican authoritites have confirmed the three people were targeted, there is no prove yet whether their link to the U.S. consulate was the cause or their identities were mistaken.

More than 2,600 drug-related deaths took place in 2009 in Ciudad Juarez making it one of the most violent cities in Mexico.

Officials from the U.S. Immigration and Customs Enforcement, the Bureau of Alcohol, Tobacco, Firearms and Explosives and El Paso County Sheriff's Office were also sent to investigate the case, a spokesman for the FBI told National Public Radio.