REFILE-UPDATE 2-US names official as US-Mexican 'border czar'

* Bersin to lead crackdown against drug-gang violence

* Named one day before Obama visits Mexico

* Three Mexican drug gangs targeted for U.S. sanctions (Fixes typo in spelling of Bersin's name, paragraph 6)

WASHINGTON, April 15 (Reuters) - The Obama administration on Wednesday named a former U.S. Justice Department official who was "border czar" during Bill Clinton's presidency to lead its efforts to crack down on drug-related violence along the U.S.-Mexican border.

Homeland Security Secretary Janet Napolitano announced the appointment of Alan Bersin, a former federal prosecutor, during a visit to El Paso, Texas.

It took place one day before U.S. President Barack Obama planned to stop in Mexico before traveling to Trinidad and Tobago for the Fifth Summit of the Americas.

The Obama administration also announced on Wednesday it was placing three Mexican drug gangs -- the Sinaloa Cartel, Los Zetas and La Familia Michoacana -- on a list of significant foreign narcotics traffickers targeted for special sanctions.

The move allows the U.S. government to freeze all cartel assets in U.S. jurisdiction and bar Americans from dealing with funds linked to the groups and their operatives.

Bersin, a former U.S. attorney in San Diego, served as the "border czar" to then-Attorney General Janet Reno during the Clinton administration. He also served as California's education secretary and superintendent of schools in San Diego.

"He will lead the efforts to make our borders safe while working to promote commerce and trade," Napolitano said in a statement.

Speaking later at a news conference in Nogales, Arizona, she added that Bersin would work as a "special envoy" facilitating cooperation among U.S. federal, state and local authorities and their Mexican counterparts.

"His ... sole mission is to make sure that all of the things happening with Mexico right now are happening in real time and producing the kinds of results that we anticipate," she said.

White House officials said on Monday that Obama's visit to Mexico was a signal of support for Mexican President Felipe Calderon and his efforts to confront violent drug trafficking gangs.

Curbing drug cartel violence is a top concern for authorities in both the United States and Mexico, where warring traffickers killed 6,300 people last year.

The U.S. government announced plans last month to help Mexican authorities combat the gangs south of the border, as well as stepping up efforts to choke off the southbound flow of U.S. guns and drug-smuggling profits to the cartels.

Napolitano said Bersin, who begins work immediately, will have the title of assistant secretary for international affairs and special representative for border affairs. (Writing by JoAnne Allen; Additional reporting by James Vicini in Washington and Tim Gaynor in Nogales; Editing by Peter Cooney)