Japanese police on Monday set up a special unit to oversee efforts to stem what they are describing as a full-fledged "war" between rival organised crime groups, media reported.
Officers have made a series of raids and arrests since late last year after a split in the country's biggest crime syndicate fuelled fears of the worst gang conflict in decades.
The Yamaguchi-gumi gang based in the western city of Kobe has been rocked by internal strife since late last year following the defection of several top leaders who formed a rival splinter group.
The split in Japan's biggest organised crime, or yakuza, organisation has prompted police warnings of a possible repeat of a 1980s gangland bloodbath.
On Monday, the National Police Agency declared that the two groups were in a state of "war against each other" and established a special headquarters to "intensify" their response, Jiji Press reported.
An agency spokesman could not immediately confirm the report, though it came as officers are investigating a spike in suspected violence involving the groups.
Two bullets were found Sunday inside an office loyal to the recently formed renegade group in the city of Mito northeast of Tokyo, a police spokesman said Monday.
Three bullet holes were also visible on a wall, but no one was injured.
The incident came after police arrested a 40-year-old gangster on suspicion that a truck he drove careened into another parked in front of the office on Saturday.
"We suspect the two cases are part of the recent conflicts" between the Yamaguchi-gumi and the splinter group, a spokesman for Mito police said.
"We are strengthening security and closely monitoring further developments," he told AFP.
A dozen similar cases allegedly involving the internecine strife have been reported since late February.
In Toyama, a prefecture on Japan's northwestern coast, a member belonging to the splinter group was arrested last week on suspicion of injuring a rival Yamaguchi-gumi gangster.
"Residents are very worried," Kenichi Tanaka, a local police official told Japan's national broadcaster NHK, after 10 police vehicles cruised around an elementary school near a gang office with which the suspect is affiliated.
"We are remaining doggedly vigilant to protect them."
Similar to the Mafia in Italy and Chinese triads, Japan's yakuza engage in everything from gambling, drugs and prostitution to loan sharking, protection rackets and white-collar crime.
But overall Japan is known for its peaceful society and low crime rates while strict firearm control laws make gun violence extremely rare, though it is often linked to organised crime gangs when it occurs.
Periodic crackdowns and police efforts to choke off Yamaguchi-gumi's sources of funding have gained momentum in recent years.
Public wariness of tolerance for organised crime and Japan's slack economy have made life difficult for gangsters and made membership less attractive for potential recruits, experts say.