A major security operation was launched in the northern English town of Barnsley after a woman attacked a man with a knife.
Police said counter-terrorism officers were helping with the investigation to establish whether it was an isolated incident and whether the suspect acted alone.
One witness said the woman pulled out a kitchen knife and shouted "kill" repeatedly as she stabbed one man in the shoulder and then walked around the streets, which were busy with market shoppers.
Police said the man suffered minor injuries.
Parts of Barnsley town centre were cordoned off as forensics officers gathered evidence.
Police urged the public to remain vigilant and appealed for witnesses.