Mexico City, Mexico (CNN) -- Authorities believe assassins targeted a pregnant woman and two other people connected with a U.S. consulate who were killed in drive-by shootings over the weekend, Ciudad Juarez Mayor Jose Reyes Ferriz said Monday.
The killings were carried out by a local gang, known as Los Aztecas, that is allied with the Juarez Cartel, Reyes told CNN. No arrests had been made by Monday afternoon.
"We know that the U.S. citizens were targeted," Reyes told CNN, saying a police officer saw gunfire from a car directed at the Americans' car. "We know they were chasing them. We know they wanted to kill them."
Two of the victims were a four-months-pregnant employee of the consulate in Juarez and her U.S. citizen husband who was a jailer in nearby El Paso, Texas, U.S. and Mexican officials said. The couple's 10-month-old child, who was in the vehicle, was not injured, Reyes and other officials said.
The child has been turned over to U.S. consular officials, Reyes said. The couple lived in El Paso, the State Department said.
The third victim, found dead in a separate vehicle, was identified as the husband of a Mexican employee of the consulate. His wife was not traveling with him, but two of their children in the car were wounded, officials said.
All the victims had left a birthday party at the consulate Saturday before they were attacked, Reyes and State Department spokesman P.J. Crowley said Monday. The slain couple, Arthur Redelfs, 34, and Lesley Ann Enriquez, 35, were on their way home to El Paso, Crowley said.
Redelfs was a 10-year veteran of the El Paso County Sheriff's Office, according to Jesse Tovar, a spokesman for the department.
Reyes said the attackers may have been confused because both groups of victims were traveling in similar-looking vehicles.
Redelfs and his wife were in a white late-model Toyota RAV4 SUV. The third victim, Jorge Alberto Salcido Ceniceros, was driving a late-model white Honda Pilot, the mayor said.
Salcido, 37, was a state police officer who was married to a Mexican employee at the U.S. consulate, Reyes said.
His two children, ages 4 and 7, were wounded and transported to a hospital, the attorney general's office said. Salcido's wife was traveling in another vehicle, which was not attacked, Reyes said.
In Washington, President Obama and Secretary of State Hillary Clinton expressed their anger.
"The president is deeply saddened and outraged by the news of the brutal murders of three people associated with the United States Consulate General in Ciudad Juarez," National Security Council spokesman Mike Hammer said in a statement Sunday. "He extends his condolences to the families and condemns these attacks on consular and diplomatic personnel serving at our foreign missions. In concert with Mexican authorities, we will work tirelessly to bring their killers to justice."
Clinton said the "safety and security of our personnel and their families in Mexico and at posts around the world is always our highest priority."
"I have spoken with our ambassador in Mexico, and we are working with the government of Mexico to do everything necessary to protect our people and to ensure that the perpetrators of these horrendous acts are brought to justice," she said.
In response to the shootings, the U.S. State Department authorized the temporary relocation of employees' families working in border-area consulates.
"These appalling assaults on members of our own State Department family are, sadly, part of a growing tragedy besetting many communities in Mexico," Clinton said in a statement Sunday night. "They underscore the imperative of our continued commitment to work closely with the Government of [Mexican] President [Felipe] Calderon to cripple the influence of trafficking organizations at work in Mexico."
The families of employees at U.S. consulates in Tijuana, Nogales, Ciudad Juarez, Nuevo Laredo, Monterrey and Matamoros are allowed to leave for 30 days "in response to an increase in violence along the Mexican side of its border with the U.S.," State Department spokesman Fred Lash told CNN.
The authorization can be renewed after 30 days, depending on a review, Lash said, adding that this was not a mandatory evacuation.
The announcement was part of a warning to U.S. citizens regarding travel to Mexico.
The warning urges U.S. citizens to delay nonessential travel to parts of the states of Durango, Coahuila and Chihuahua, where Juarez is located, because of "recent violent attacks." U.S. government employees are restricted from traveling to all or parts of these three states.
Attacks include the kidnapping and killing of two resident U.S. citizens in Chihuahua, the warning states.
"Some recent confrontations between Mexican authorities and drug cartel members have resembled small-unit combat, with cartels employing automatic weapons and grenades," the warning says. "During some of these incidents, U.S. citizens have been trapped and temporarily prevented from leaving the area."
Reyes, who received a death threat last week, said the shootings highlight a problem shared by both countries along their 2,000-mile border.
"It is not just a Mexican problem -- it's is a U.S.-Mexico problem," Reyes said. "I'm very glad that the U.S. has taken that position."
He said that he supported the State Department's authorization to consular families and that "it is important they feel safe."
Mexico said Sunday that it was committed to protecting all people, citizens and visitors alike, diplomats or not.
"The Mexican government deeply laments the killings of three people linked to the U.S. Consulate in Ciudad Juarez," Mexico's foreign ministry said in a statement. "The Mexican authorities are working with determination to clear up the facts surrounding the crime scene and put those responsible before the law."
Juarez is one of the front lines in Mexico's war against the drug cartels that operate in its territory. More than 2,600 people were killed in Juarez in 2009.
The city has become a focal point of Calderon's anti-drug efforts after the January 31 killings of 15 people there, most of whom were students with no ties to organized crime. The incident sparked outrage across Mexico.
But the violence is not restricted to Juarez.
In the western state of Guerrero, at least 25 people were killed Saturday, state officials said.
The bodies of 14 people, including nine civilians and five police officers, were found in various parts of the resort city of Acapulco, the official Notimex news agency reported, citing Guerrero Public Security Secretary Juan Heriberto Salinas.
In the small city of Ajuchitlan del Progreso, 10 civilians and one soldier were killed in two shootouts that started when federal officials tried to execute search warrants at two locations, Salinas said.
Police in the state were on a heightened security alert, he said.
The government has not released official figures, but national media say 7,600 Mexicans lost their lives in the war on drugs in 2009. Calderon said last year that 6,500 Mexicans died in drug violence in 2008.
Unofficial tallies this year say more than 16,000 people have been killed since Calderon declared war on the cartels after assuming office in December 2006.
CNN's Arthur Brice, Mariano Castillo and Jamie Crawford contributed to this report.