WASHINGTON, June 5 (Reuters) - The U.S. government said on Tuesday it will appeal a federal judge's ruling that dismissed immigration fraud charges against anti-Castro Cuban exile and former CIA operative Luis Posada Carriles.

The Justice Department filed a brief notice of appeal with U.S. District Judge Kathleen Cardone in El Paso, Texas, in response to the judge's surprise ruling last month.

Just days before he was set to go on trial, Cardone dismissed the immigration charges against Posada Carriles, 79, on grounds that the U.S. government case was based on statements it got from the defendant under false pretenses.

Posada Carriles is wanted in Cuba and Venezuela, where he is accused of masterminding the 1976 bombing of a Cuban airliner that killed 73 people.

Cuban leader Fidel Castro and Venezuelan President Hugo Chavez have criticized Washington for having a double standard in its war on terror, saying Posada Carriles should be charged with terrorism and murder, not immigration crimes.

Venezuela has sought his extradition for trial in the airline bombing, which occurred while Posada Carriles, a naturalized Venezuelan, lived there.

Posada Carriles had been in U.S. custody since May 2005 after he entered the country illegally and sought asylum.

In January, he was indicted on seven immigration fraud charges. He is accused of lying to immigration authorities.

Along with the plane bombing, he is accused in Cuba of plotting a series of 1997 hotel bombings in Havana that killed an Italian tourist.

He was jailed in Panama for plotting to kill Castro during an Ibero-American summit in 2000, but was pardoned by outgoing President Mireya Moscoso in 2004.

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