(Reuters) - Former Boston mob boss James "Whitey" Bulger has asked the U.S. Supreme Court to review his 2013 conviction for committing or ordering the murders of 11 people while he ruled the city's underworld in the 1970s and 80s.

Bulger's attorneys deployed a novel strategy at his racketeering trial, admitting on the first day that their client, now 86, had been an "organized criminal" and focusing most of their energy on denying he had ever served as a law enforcement informant, or "rat" in mob parlance.

Last year they argued that Bulger had been denied justice because he had not been allowed to testify that a now-dead former U.S. prosecutor gave him immunity for his crimes in exchange for protection.

U.S. District Judge Denise Casper had blocked that claim on the grounds that no immunity deal could allow a suspect to legally commit murder, and in March the First Circuit upheld the original verdict.

A court filing made public on Wednesday does not lay out the reasoning for Bulger's latest appeal, but merely seeks the top court's attention.

The Supreme Court declines to hear the vast majority of cases brought before it, meaning the odds are that Bulger's appeal will have little effect.

Bulger is currently serving a life term without possibility of parole at a federal penitentiary in Sumterville, Florida.

Several members of Bulger's notorious "Winter Hill" gang testified against their old boss during his trial under deals with federal prosecutors that protected them from arrest.

Bulger's trial highlighted a dark time in Boston's history, when FBI agents who shared his Irish ancestry turned a blind eye to his gang's reign of murder and mayhem, in exchange for information they could use against the Italian-American mafia, then a top target for federal prosecutors.

But Bulger always denied providing information to law enforcement, insisting that he paid agents for tips while providing none.

Bulger fled the city in 1994 on a tip that his arrest was imminent. He spent 16 years on the lam, many listed atop the FBI's "Most Wanted" list, before his capture in Santa Monica, California, in 2011.

"Black Mass," a book on Bulger's rise to power and eventual flight was turned into a 2015 film starring Johnny Depp as the gangster.

(Reporting by Scott Malone; Editing by Tom Brown)