President Barack Obama is "outraged" by the murders in Ciudad Juarez, Mexico of three people connected with the US consulate there, a White House official said on Sunday.
"In concert with Mexican authorities, we will work tirelessly to bring their killers to justice," White House National Security Council spokesman Mike Hammer said in a statement.
A consulate employee and her husband, both US citizens, were killed along with the husband of another employee who is a Mexican citizen, the statement said.
"The president is deeply saddened and outraged by the news," Hammer said, adding that Obama "shares in the outrage of the Mexican people at the murders of thousands in Ciudad Juarez and elsewhere in Mexico.
Mexico's drug war has killed some 18,600 people, mainly cartel members and police officers, since President Felipe Calderon took power and launched an army crackdown on traffickers in late 2006. The rampant violence worries Washington and foreign investors.
Hammer said the United States would work with Calderon's government "to break the power" of drug trafficking organisations.