LONDON (AP) — London police are searching for a man who is believed to have stabbed four people in a series of unprovoked attacks.

The Metropolitan Police Service says two of the victims are in critical condition. Officers are warning there will be increased police activity in the Edmonton area of north London after the four attacks, which occurred over 15 hours Saturday night and Sunday morning.

Police say the attacks are not terror-related.

Detective Chief Inspector Stuart Smillie says the victims "appear to have been selected at random" because they were alone and vulnerable.

The attacks come amid an escalation of knife-related crime in Britain. Authorities have announced that some police forces have been given greater powers to stop and search suspects without reasonable suspicion in an effort to stop future attacks.