Updated

TIJUANA, Mexico -- Two men killed by a gunman who opened fire while they waited in line to reach a Tijuana border crossing were U.S. citizens, a diplomat said Tuesday, and their San Diego employer described them as diligent workers who had moved to the Mexican border city so they could afford to live on the beach.

U.S. Consulate spokesman Joseph L. Crook said the men were waiting in line in their vehicle early Monday almost half a mile (almost a kilometer) from the San Ysidro crossing, one of the world's busiest ports of entry.

"Our condolences go out to their families at this difficult time," the consulate said in a statement. "We are working closely with the Mexican authorities to ascertain all of the facts."

He did not release their names, saying officials were still trying to contact their families.

More than 34,000 people, including an increasing number of U.S. citizens, have been killed in Mexico's drug war but shootings of people waiting in line to cross into the United States are extremely rare.

Prosecutors in Baja California state quoted witnesses as saying a gunman approached the line and fired into the men's pickup truck, hitting the victims in the head, arms and body. Both victims were dead by the time authorities arrived.

Police found 9-mm shell casings at the scene, authorities said. That ammunition is used in weapons favored by drug cartel gunmen in Mexico.

Matt Pelot of San Diego-based West Coast Beverage Maintenance, confirmed the victims were his employees: Kevin Romero, 28, and Sergio Salcido, 25.

He said Romero's sister called him Monday morning to tell him they had been killed.

"She just said I just wanted to let you know that Sergio and Kevin were shot and killed this morning at the border, and obviously I was taken back," he said. "I was in shock, and I'm still in shock. These were good guys. Obviously no one deserves to die like this, but these were good guys."

The men, who were good friends and had worked for Pelot for more than a year, were crossing around 2:40 a.m. as they usually did to beat the long lines that form later in the morning when thousands cross to go to work or school on the U.S. side, Pelot said. They had moved to Tijuana because of the lower cost of living.

Romero's parents live near the border on the U.S. side and the men would go there to sleep before heading in to work. The two maintained draft beer systems at restaurants and bars in the San Diego area and were always eager to work overtime for the small company, which has 13 employees, Pelot said.

Pelot said he was just thinking of promoting Romero, who was originally from San Diego. Romero was trying to adopt his Mexican girlfriend's son and move them to the United States someday, while Salcido, he said, was a single guy who was born in Tijuana to U.S. citizens and grew up in Bakersfield, Calif. He said Salcido loved martial arts and was training for an upcoming bout in Tijuana.

"Kevin Romero didn't even drink beer," Pelot said. "These guys weren't dealing drugs that's for sure. If Sergio was your friend, he'd give you the shirt off his back. Kevin was the same. He was a real family oriented guy who couldn't wait to get home and take a walk on his beach with his son and dogs."

Pelot said his employees had invited him to visit them in Tijuana but he was too afraid to cross the border because of the city's violence.

In the first six months of 2010, the latest State Department figures available, 49 Americans were victims of homicide in Mexico, up from 37 for the same period in 2009 and 19 in the first half of 2008.

The majority of the slayings happened in border cities such as Ciudad Juarez and Tijuana, which have also been the hardest hit by drug violence. In some cases, the Americans apparently were in the company of Mexican friends, relatives or acquaintances who were the targets.

Other Americans have been killed by stray bullets, and in at least one case, Americans were directly targeted by a drug gang: U.S. consular employee Lesley A. Enriquez and her husband, Arthur H. Redelfs, who were gunned down in their white SUV on a Ciudad Juarez street March 13, 2010.