A police officer shot to death late Tuesday in Los Angeles County was killed while serving a warrant as part of an investigation into a feud between rival motorcycle gangs, law enforcement sources tell NBC News.

The slain officer, Shaun Diamond of the Pomona Police Department, was hit with a single shotgun blast to the neck late Tuesday at one of a half-dozen locations where a multi-agency outlaw motorcycle gang task force was serving search warrants, according to the sources, who spoke on condition of anonymity. Authorities arrested David Martinez, 36, of San Gabriel, California, whom multiple sources described as a full member of Mongols Motorcycle Club.

The sources said that police were moving to head off retaliation by the Mongols against members of their longtime rival Hells Angels, an outlaw biker gang founded in the 1950s, as well as a sport bike club known as the G-Zer (pronounced “geezer”) Tribe, based in the East Los Angeles area.

The motive for the payback appears to stem from at least two recent encounters between members of the three gangs on Los Angeles and Riverside County freeways in which Mongols members were shot at or pushed off their bikes. At least one Mongol member was killed, another was paralyzed and several others were wounded in the incidents, according to the sources.

Police also have become increasingly concerned about interactions between the more established outlaw motorcycle gangs (OMGs) like the Mongols and Angels and the newer sport clubs, also known as “pocket-rocket” and “crotch rocket” gangs, as well as the potential recruitment of those riders into the older gangs. Part of the broader investigation is looking at whether the Mongols tried to coerce G-Zer Tribe members into paying dues or associating solely with their gang, the sources said.

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The sport biker groups, which have grown significantly since the 1990s, typically skew younger and more ethnically diverse than the outlaw gangs. They’re best known for executing brazen maneuvers on sleek, high-performance motorcycles as they speed down busy freeways and city streets. Some of those tricks, which have gone viral via GoPro camera video and social media, have sparked altercations with motorists and the law.

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Jorja Leap, a professor of social welfare at UCLA and a nationally recognized gang expert, said there is still a big difference between the hardcore biker gangs and the more “recreational" sport bike gangs, who are reluctant or even unwilling to engage in illegal activities and violence.

“They are almost like recreational drug users in that they are playing with it but they are not hardcore,” Leap said. “One or two of them may tip over, just like addicts, but the vast number of individuals are doing it recreationally. It’s like taggers are to gangs.”

However, New York City police arrested several men last year after video surfaced on the web of a group of sports bikers surrounding and beating an SUV driver in Manhattan.

On the other hand, ATF agents have called the Mongols “the most violent and dangerous OMG in the nation.”

The gang operates primarily in the Southwest and along the Pacific Coast and some members have been involved in cocaine, marijuana and methamphetamine trafficking, extortion, robbery and money laundering, federal officials said. According to officials, the membership of about 2,000 is largely Latino and concentrated in Greater Los Angeles.

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A 2008 indictment of leaders and members of the gang noted that the Mongols have a long history of conflict with rival motorcycle gangs and criminal groups like the Mexican Mafia, sometimes over the control of narcotics trafficking.

In one particularly brazen incident detailed in the case, Mongols members allegedly shot Hells Angels members and an off-duty firefighter on Dec. 4, 2005, as they attempted to collect donations at a “Toys for Tots” event in Norco, California.

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There are more than 300 active OMGs within the United States, ranging in size from single chapters with five or six members to massive clubs with hundreds of chapters and thousands of members worldwide. The U.S. Department of Justice says that “the Hells Angels, Mongols, Bandidos, Outlaws, and Sons of Silence pose a serious national domestic threat and conduct the majority of criminal activity linked to OMGs, especially activity relating to drug-trafficking and, more specifically, to cross-border drug smuggling.”

Leap said the current investigation into potential retaliatory violence involving the Mongols may “shed more light on how extensive and how dangerous the nature of alleged ‘taxation’ of sports club bikers actually is.”

“For now we are left we are left with a tragedy and many questions,” Leap said.