Japanese authorities have arrested three people accused of posting Internet messages warning they would commit crimes including murder, local news media reported Monday.

The messages mimic those posted prior to a violent attack in Tokyo's Akihabara district that left seven people dead and 10 injured on June 8.

Suspect Tomohiro Kato, who allegedly rammed a rented truck into a crowded street, then jumped out and began stabbing people with a dagger, repeatedly wrote of his plans online beforehand. He was arrested at the scene with his bloodstained weapon, and police say he has confessed.

The latest arrests reportedly include an unemployed 29-year-old man who police say posted on a popular Japanese Web site "I'm sick of it all. I'm going to do it too" and wrote he was going to "kill 100 people" in Ikebukuro, a crowded shopping and business area of Tokyo.

Similar messages have repeatedly been posted in the days since the Akihabara attack, and authorities have made arrests where specific locations were mentioned, the Yomiuri newspaper reported.

A total of three people have been arrested for such postings, according to Kyodo News agency.

Authorities at Japan's National Police Agency could not immediately be reached for comment.

Police have monitored the Internet closely since the rampage. Kato posted hundreds of messages from his mobile phone, including some 30 postings the day of the attack, ending with "It's time" just 20 minutes before the killings.

Japanese authorities have been increasingly concerned about Internet abuse, especially sites with suicidal posters and others who encourage them.

In the midst of a spike in suicides where people kill themselves by mixing household chemicals to produce deadly gas, Japan's National Police Agency has urged Internet providers to delete materials from Web sites showing readers how to mix the chemicals.